^SP^ 

'TVT?. P  ?T1 


REPORTS  OF  OBSERVATIONS 


OF  THE 


TOTAL  ECLIPSE  OF  THE  SUN. 


A.  UaiJ  SIT    7,   11869, 

MADE   BY  PARTIES   UNDER  THE   GENERAL  DIRECTION  OP 

PROFESSOR  J.  H.  C.  COFFIN,  U.  S.  N., 

SUPERINTENDENT   OF   THE    AMERICAN   EPHEMEBIS    ANDJ  NAUTICAL    ALMANAC. 


PUBLISHED  BY  AUTHORITY  OF  THE  SECRETARY  OF  THE  NAVY. 


I 

u 


TABLE   OF    CONTENTS. 


Page. 

REPORT  OF  PROFESSOR  COFFIN'  TO  THE  SECRETARY  OF  TUB  NAVY 

GENERAL  REPORT  OF  PROFESSOR  COFFIN    -- 

Latitude  and  longitude  <if  Coast  Survey  Station,  Burlington,  Iowa 

Local  times:  Chronometers;  chronometer  corrections 

REPORT  OF  PHOFF.SSOR  COFFIN,  BURLINGTON,  IOWA: 

Position  of  eclipse  station.  Burlington  

Preparations  for  the  eclipse 

Arrangement  of  the  party "" 

Meteorological  oliservations ^ 

Observations  of  the  eelipse -• 

First  contaet;   notes  of  the  eelipse;   total  obscuration ;  the  C'trona  ;   prominenees;  last  contact 22-2f> 

Collected  results  of  the  several  observers  at  P.iirlington  (loeal  mean  ti  i  es  at  the  stations  occupied) 2<i 

RKPORT  OF  l)i!.  Gori.n,  HUUI.INGTON 

First,  con  tar  I  :   the  corona  and  prominences 30 

Last  contact 

Supplementary  report "*6 

REPORT  OF  PROFESS.  >u  You.vo,  BURLINGTON   

Instruments 41 

Preliminary  operations , 

Lunar  prominence;  first  contact  determined  by  the  spectroscope 43 

Lunar  atmosphere 

Spectrum  lines  observed  during  totality 

Polarization ;  general  impressions 

Last  contact . . 

Comparison  of  the  spectra  of  the  corona  and  the  aurora  borealis 

Results - so 

Observation  of  the  eclipse  at  Hanover,  N.  H.,  by  Lewis  Boss 'r>l 

REPORT  OF  Miss  MITCHELL  AND'IIEU  ASSISTANTS,  BURLINGTON 

REPORT  OF  MR.  STOCKWELL 

REPORT  OF  PROFESSOR  EATON 

REPORT  OF  MR.  WIESSNER 

Geographical  positions  of  Mount  Pleasant,  Iowa;  Kewanee,  111.  ;  and  Monroe,  Mo  (>9-71 

Observations  of  the  eclipse  at  Monroe   

REPORT  OF  Mu.  AUSTIN,  KEWANEE,  ILL 7:< 

REPORT  OF  PROFESSOR  WATSON,  MOUNT  PLEASANT,  IOWA 79 

Chronometer  corrections 

Observations  of  the  eclipse  ;  collected  results 

REPORT  OF  PROFESSOR  VAN  VLKCK,  MOUNT  PLEASANT,  IOWA 

Contacts 

Spectroscopic  observations 

REPORT  OF  PROFESSOR  PICKERING,  MOUNT  PLEASANT,  IOWA 

The  total  phase;  observations  with  the  spectroscope  and  polariscopc 

Note  on  the  supposed  polarization  of  the  corona 

REPORT  OF  PROFESSOR  ALEXANDER,  OTTCMWA,  IOWA 

Observations  of  the  eclipse 

The  corona  and  its  appendages 10o 

Other  observations 

Thermometer  and  barometer  observations  .    

Observations  for  latitude 

Supplementary  report  of  Professor  Cofiin;   latitude  and  longitude  of  Ottumwa Ill 

i 


ii  TABLE  OF  CONTEXTS. 

1{KI>ORTS  OK  THE  PHILADELPHIA    I'lIOTOCiHArillC    Kxi'EIMTIl  >X 11") 

«  liKi-oRT  OK  PUOKKSSOR  MOHTO.V 11"' 

*  Distribution  of  parlies Ht> 

Arrangement  (if  i list rii iiic-iits  f.ir  photographic  work Ill) 

Preparations 117 

Partial  phase  pictures  1-1 

Totality  pictures -  !-•> 

The  corona 125 

b  KBPORT  o*  PROFKSSOU  MAYHR,  BCRIINGTOS  I'-i'J 

Preparatory  work 12i) 

Position  ami  ill-script  ion  of  the  si  at  inn  1  •'>(.) 

The  equatorial  anil  irs  adjustments;  prcliminai-y  adjust  men t  without  the  aid  of  stars 1H1 

The  camera  and  chronograph 132 

Work  during  the  eclipse 135 

Description  of  the  photographs K!7 

Results  U4 

Position-angles,  and  heights  of  the  prominences 14") 

Measurements  on  I  he  solar  spot  iu  the  southwest  quadrant 14S 

Oti  the  application  of  photography  to  observations  of  the  transits  of  Venus  in  1>74  and  lf^ 14-< 

c  RKPOKT  OF  PKOKKSSOK  HIMKS,  OTTUMWA 151 

Instruments  and  station  151 

Times  and  exposure  of  the  photograph ie  plates 154 

NOTE  ON  PHOTOllUAl'lIIXli  THE  COIJOXA.      BY  PUOKK.SSOH   PlCKEKlXti 15(i 

SUPPI.KMKXTAUY  NoTK  MY  PROFESSOR  L'ol  I  IX  ON  TIIK  lifHLIXOTOX  PlH)TO(iUAl>lIS 157 


.DESCIUPTIOX  OF  THE  PLATES. 


PLATK         I. — Fig.  1.  Corona  and  prominences,  as  seen  in  field  of  the  telescope,  by  Professor  Coffin. 

Fig.  2.  C'onma  iind  prominences,  liy  Professor  Watson. 

Figs.  :!  and  -I.    Daily's  beads,  liy  Professor'Watson. 
PLATE       II. — Three  views  of  the  Orona  and  prominences,  by  Dr.  Gould  (the  position-angles  of  the  prominences  are 

taken  from  Professor  Mayer's  description  and  diagram). 
PLATE     III. — Fig.  1.  Solar  spectrum,  by  Professor  Young. 

Fig.  -2.  Spectrum  (if  lines  at  first  contact,  by  Professor  Young. 

PLATE      IV. — From  photograph  plate  24.  Burlington,  18s  after  beginning  of  totality. 
PLATK        V. — From  photograph  plate  is,  Ottutmva,  44"  after  beginning  of  totality. 
PLATE      VI. — From  photograph  plate  I'.l.  Ottnnnva,  lm  31"  after  beginning  of  totality. 
PLATE    VII. — From  photograph  plate  27,  .Burlington,  I"1  57"  after  beginning  of  totality. 
PLATE  VIII. — From  pholngraph  plate  '20,  Ottnmwa,  28"  before  end  of  totality. 
PLATE      IX. — Enlarged  photograph  of  solar  crescent,  plate  21,  Burlington. 
PLATE       X. — Fig.  1.   Diagram  ofihe  prominences,  by  Professor  Mayer. 

Fig.  2.  Lunar  mountain,  from  photograph  plate  Ifi,  Burlington,  by  Professor  Mayer. 

Fig.  3.  Solar  spot,  from  photograph  plate  4,  Burlington,  by  Professor  Mayer. 

Fig.  4.  Solar  spot,  from  photograph  plate  44,  Burlington,  by  Professor  Mayer. 

Hi 


NAUTICAL  ALMANAC  OFFICE, 

Washington,  March  31,  1870. 

SIR  :  In  response  to  recommendations  in  my  annual  report  in  October,  1 868,  and 
the  representations  of  the  American  Academy  of  Arts  and  Sciences  in  Boston,  the 
American  Philosophical  Society  and  the  Franklin  Institute  in  Philadelphia,  and  of 
others  interested  in  the  promotion  of  science,  Congress  appropriated  $5,000  "for 
observations  of  the  eclipse  of  the  sun  in  August,  1869,  under  the  direction  of  the 
superintendent  of  the  Nautical  Almanac." 

The  appropriation  was  desired  "  for  defraying  expenses  of  observers,  of  moving 
instruments  of  sufficient  power  to  the  line  of  central  eclipse,  and  of  preparing  for  abun- 
dant photographic  records  and  spectroscopic  observations." 

I  have  the  honor  to  present  the  accompanying  reports  of  the  observations  of  the 
several  parties  organized,  or  aided,  under  this  authority. 

After  ascertaining  how  other  important  positions  were  provided  for,  and  the  dis- 
tribution of  observers,  and  on  consulting  with  the  committee  of  the  National  Academy 
of  Sciences,  of  which  Prof.  Stephen  Alexander,  of  the  College  of  New  Jersey,  was 
chairman,  I  selected  Burlington,  Iowa,  as  the  principal  station.  The  determination 
of  its  geographical  position  was  provided  for  by  Prof.  Benjamin  Peirce,  Superintendent 
of  the  United  States  Coast  Survey. 

Appreciating  the  importance  of  photographs  of  this  eclipse  "  taken  with  all  the 
sharpness  of  definition  which  the  art  admits  of,"  and  "  with  a  precision  which  will 
admit  of  microscopic  measurement,"  I  requested  Prof.  Henry  Morton,  Ph.  D.,  secre- 
tary of  the  Franklin  Institute  in  Philadelphia,  to  undertake  the  organization  and  direc- 
tion of  a  party  for  the  purpose.  Entering  into  it  with  characteristic  zeal,  he  soon 
enlisted  as  volunteers  in  this  work,  from  among  the  best  photographers  in  Philadel- 
phia, a  sufficient  number  to  form  three  parties. 

Col.  Thomas  A.  Scott,  vice-president  of  the  Pennsylvania  Central  Railroad,  fur- 
nished a  special  car,  and  with  the  cordial  co-operation  of  Mr.  Robert  Harris,  general 
superintendent  of  the  Chicago,  Burlington  and  Quincy,  and  Mr.  C.  E.  Perkins,  of  the 
Burlington  and  Missouri  Railroad,  provided  free  transportation  for  these  parties,  with 
all  their  instruments  and  apparatus,  to  and  from  the  places  of  observation.  Free 
passes  to  ten  or  twelve  others,  over  these  same  routes,  were  also  granted ;  and  return- 
tickets  to  several  from  Chicago  to  Buffalo,  over  the  Michigan  Southern  and  Lake 
Shore  Roads,  and  from  Chicago  to  Pittsburgh  by  the  Pan-Handle  Route.  Such  liber- 
ality, in  aid  of  a  scientific  work,  needs  but  to  be  mentioned  to  insure  for  it  a  cordial 
appreciation. 

The  trustees  of  the  Philadelphia  Central  High  School,  of  Pennsylvania  College 
in  Gettysburg)!,  and  of  the  University  of  Pennsylvania  in  Philadelphia,  kindly  granted, 
at  my  request,  the  use  of  their  telescopes.  Those  of  the  two  former  institutions  were 


4  EOLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

each  of  6.4  inches  aperture,  and  furnished  with   clock-motion,  and  thus  were  well 
adapted  for  photographing  the  total  phase  of  the  eclipse. 

I  am  indebted  to  Commodore  B.  F.  Sands,  U.  S.  N.,  Superintendent  of  the  Naval 
Observatory,  Washington,  for  a  supply  of  chronometers,  and  to  him  and  Vice-Admiral 
D.  D.  Porter,  U.  S.  N.,  Superintendent  of  the  United  States  Naval  Academy,  for  such 
other  needed  instruments  as  those  institutions  could  supply. 

My  acknowledgments  are  also  due  to  Mr.  J.  J.  S.  Wilson,  superintendent  of  the 
Western  Union  Telegraph  Company,  at  Chicago,  and  to  the  operators  at  the  several 
stations,  for  the  free  use  of  their  lines  for  comparison  of  chronometers,  and  such  com- 
munications as  our  work  required. 

With  these  aids,  I  was  enabled  to  provide  for  three  stations  near  the  central  line, 
instead  of  one,  as  originally  contemplated,  and  I  thought  it  best  thus  to  divide  the 
parties  and  diminish  the  chance  of  failure  from  clouds  or  other  unfavorable  circum- 
stances. 

Associated  with  me  at  Burlington,  Iowa,  were — 

Dr.  B.  A.  Gould,  of  Cambridge,  Mass.,  chiefly  for  observation  and  measurement 
of  the  corona,  and  search  for  intra-Mercurial  planets ; 

Prof.  Charles  A.  Young,  of  Dartmouth  College,  New  Hampshire,  for  spectroscopic 
observations ;  and 

Prof.  Alfred  M.  Mayer,  Ph.  D.,  of  the  Lehigh  University,  Bethlehem,  Pa.,  in 
charge  of  the  photographic  party,  with 

Mr.  O.  H.  Willard,  of  Philadelphia,  as  photographer. 

Miss  Maria  Mitchell,  professor  of  astronomy  in  Vassar  College,  Poughkeepsie, 
N.  Y.,  was  also  at  Burlington  for  astronomical  observations,  but  occupied  a  station  in 
a  different  part  of  the  city. 

At  Mount  Pleasant,  Iowa,  28  miles  to  the  westward,  on  the  Burlington  and  Mis- 
souri Railway,  were  stationed — 

Prof.  James  C.  Watson,  director  of  Ann  Arbor  Observatory,  University  of  Michi- 
gan, for  astronomical  observations ; 

Prof.  J.  M.  Van  Vleck,  of  the  Wesleyan  University,  Middletown,  Conn.,  for  spec- 
troscopic observations ; 

Prof.  Henry  Morton,  Ph.  D.,  of  the  Franklin  Institute,  in  Philadelphia,  in  charge 
of  the  photographic  party,  with 

Mr.  Edward  L.  Wilson,  of  Philadelphia,  as  photographer. 

Prof.  Edward  C.  Pickering,  Ph.  D.,  of  the  Massachusetts  Institute  of  Technology, 
Boston,  was  also  associated  with  this  party  for  physical  observations. 

At  Ottumwa,  Iowa,  75  miles  from  Burlington,  Iowa,  on  the  same  railroad,  were — 

Prof.  Stephen  Alexander,  of  the  College  of  New  Jersey,  Princeton,  for  astronomi- 
cal and  physical  observations ;  and 

Prof.  Charles  F.  Himes,  Ph.  D.,  of  Dickinson  College,  Carlisle,  Pa.,  in  charge  of 
the  photographic  party,  with 

Mr.  J.  Zentmayer,  of  Philadelphia,  as  chief  photographer. 

The  names  of  the  assistants  connected  with  these  several  parties  will  be  found  in 
the  separate  reports  of  each. 


REPORT  OF  PROFESSOR  COFFIN.  5 

Prof.  James  McClure,  of  the  Philadelphia  Central  High  School,  and 

Prof.  S.  G.  Gummere,  of  Haverford  College,  Pennsylvania,  also  accompanied  the 
expedition,  and  went  forward  to  Oscaloosa,  25  miles  beyond  Ottumwa. 

Mr.  E.  P.  Austin  and  Mr.  John  Weissner,  assistants  in  this  office,  were  dispatched, 
respectively,  to  Kewanee,  in  Illinois,  and  Monroe,  in  Missouri,  near  the  limits  of  the 
shadow,  for  observing  specially  the  duration  of  totality. 

The  reports  of  these  several  parties  are  all  replete  with  interest ;  they  show  how 
abundantly"  successful  all  have  been,  and  how  faithfully  and  earnestly  each  one.  per- 
formed his  allotted  part.  The  kind  feeling  and  cordial  co-operation  of  all  in  a  work 
of  common,  yet  varied,  interest,  is  gratefully  remembered. 

The  rich  materials  contributed  in  general  observations  and  notes  on  the  corona, 
by  Dr.  Gould ;  in  spectral  analysis,  by  Professor  Young ;  and  in  photography,  by  the 
"  Philadelphia  Photographic  Expedition,"  organized  by  Professor  Morton,  are  espe- 
cially valuable. 

Professor  Young's  novel  method  of  observing  contacts  in  an  eclipse,  by  means 
of  a  spectroscope,  has  attracted  much  attention. 

The  collection  of  photographs  is  invaluable.  Those  taken  during  the  totality  are 
described  in  this  volume,  and  engravings  of  several  of  them  given.  The  others  are 
yet  to  be  subjects  of  measurement  and  study. 

It  is  regretted  that  the  means  at  command  allow  only  a  limited  distribution  of 
photographs. 

I  have  added  reports  from  several  others,  besides  those  who  were  formally  con- 
nected with  these  parties,  and  extracts  from  communications  made  to  me  of  observa- 
tions in  other  places. 

I  have  the  honor  to  be,  sir,  very  respectfully,  your  obedient  servant, 

J.  H.  C.  COFFIN, 
Professor  of  Mathematics,   U.  S.  N., 

Superintendent  of  Nautical  Almanac. 
Hon.  GEORGE  M.  ROBESON, 

Secretary  of  the  Navy. 

NOTE.— Failing  health,  culminating  in  a  severe  illness  in  the  early  part  of  1871  and  subse- 
quent nervous  prostration,  led  me  to  lay  aside  these  reports  and  the  requisite  computations. 
Those  who  have  similarly  suffered  know  how  hard  it  is,  amid  other  occupations,  to  resume  work 

long  deferred. 

J.  H.  0.  C. 

AUGUST,  1877. 


REPORT 


OF 


PROFESSOR  JOHN  H.  C.  COFFIN,  U.  S.  N.f 


BTJRLIISI 


REPORT  OF  PROF.  JOHN  H.  C.  COFFIN,  U.  S. 


THE 


BURLINGTON,  IOWA.  W  '  V  E  R  *™ 

LOCATION    AND    GEOGRAPHICAL    POSITION. 

Burlington  is  on  the  west  side  of  the  Mississippi  River,  about  1,540  miles  from  its 
mouth.  It  is  situated  chiefly  on  the  top  and  sloping  sides  of  bluffs,  which  rise  in  some 
places  abruptly  from  the  river  and  are  divided  by  a  rugged  ravine. 

Its  geographical  position  was  determined  at  my  request  by  parties  of  the  United 
States  Coast  Survey  under  the  direction  of  Assistant  K.  Goodfellow.  The  observa- 
tions at  Burlington  were  made  by  Mr.  K.  P.  Austin.  The  instruments  which  he  used 
were  Wtirdemann's  portable  transit-instrument  No.  6,  belonging  to  the  Naval  Acad- 
emy, sidereal  chronometer  Hutton  202,  and  for  latitude  a  zenith  telescope  furnished 
by  the  Coast  Survey.  The  same  transit  instrument  and  chronometer  were  used  sub- 
sequently at  the  same  station  during  the  period  of  the  eclipse. 

The  station  occupied  was  in  a  public  reservation  on  South  Hill,  in  the  southern  - 
part  of  the  city,  and  about  200  feet  south  of  Saint  John's  (Roman  Catholic)  Church. 
The  stone  pier  of  the  transit-instrument  remains  to  mark  the  spot. 

The  longitudes  from  Burlington  and  the  Burlington  times  in  the  following  reports 
refer  to  this  point. 

The  latitude  of  this  station,  obtained  from  observations  with  the  zenith  telescope 
of  20  pairs  of  stars  on  5  different  nights,  was  found  to  be 

+  40°  48'  23".o9  ±o".2i; 

its  longitude,  by  comparison  of  chronometers  by  means  of  the  electric  telegraph, 

1869,  June  17,          19™  20".  10 

21,  20 .28 

22,  20.31 


19    20.23 

east  of  the  Coast  Survey  station  at  Omaha  in  Nebraska.  The  chronometer-corrections 
at  the  two  stations  were  determined  by  observations  with  portable  transit-instruments 
on  the  same  nights. 

From  previous  determinations  under  the  Coast  Survey,  by  means  of  the  electric 
telegraph,  we  have 

Omaha,         ih  39™  I5".O7*  west  of  Cambridge,  Mass. 
Cambridge, o    23    41.11    east  of  Washington  ; 

whence  Burlington,  o    56    13  .73  =  14°  3'  26"o.  west  of  Washington; 
or,  6      4    25  .8-2  —  91     6    27  .3  west  of  Greenwich. 

*  Report  of  United  States  Coast  Survey,  1870,  pp.  100,  104. 
2  E   S 


10 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


LOCAL    TIMES CHRONOMETERS. 

Subsequently,  the  same  transit-instrument  was  remounted  by  Mr.  Austin  in  the 
same  position,  and  the  following  corrections  found  for  sidereal  chronometer  Hutton 
202,  with  which  the  other  chronometers  of  the  expedition  were  compared  directly  or 
by  telegraph. 

The  transit-instrument  was  reversed  and  stars  observed  in  both  positions  on 
each  night,  except  that  of  August  6,  astronomical  day,  when  the  unfavorable  circum- 
stances of  clouds,  rapidly-approaching  daylight,  and  the  necessity  of  other  prepara- 
tions for  the  eclipse  prevented  the  completion  of  the  intended  series  of  observations. 
The  collimation-correction  was  found  to  be  nearly  constant ;  but  the  instrument  lacked 
stability  in  level  and  azimuth,  so  that  adjustments  were  usually  necessary  at  the  com- 
mencement of  each  night's  work.  The  changes  of  level,  determined  by  the  spirit-level, 
were  not  very  great  during  any  night ;  but  those  of  azimuth  were  decidedly  manifest. 
Prof.  Reuel  Keith,  formerly  of  the  Washington  Observatory,  who  reduced  these  obser- 
vations, has  carefully  discussed  these  changes,  and  deduced  for  each  night  the  most 
probable  result  Inequality  of  pivots  has  been  taken  into  account. 

Corrections  of  sidereal  chronometer  Hutton  202. 

Referred  to  sidereal  time  of  Burlington  C.  S.  station. 


No.  of  stars  for  — 

Burlington 
mean  time. 

Chron. 
time. 

Chron. 
correction. 

Daily  change. 

Irregularity. 

Observer. 

,  .. 

Time. 

Az. 

1869.         h. 

h. 

m.       s. 

s. 

s. 

July  29      9.7 

18 

+  ii     9-3 

+  5-1 

+       0.3 

4 

3 

Mr.  Austin. 

30      9.6 

18 

ii   M-4 

5-5 

+       0.6 

4 

2. 

Do. 

3i      9-5 

18 

ii   19.9 

+       0.6 

4 

3 

Do. 

Aug.  2      9.4 

18 

ii  31.2 

'6.6 

+       0.3 

6 

4 

Do. 

3      9-4 

18 

ii  37-8 

6.0 

-       0.9 

6 

3 

Do. 

4      9-3 

18 

II  43-8 

5.3] 

—       1-5 

5 

2 

Do. 

6    14.7 

24 

ii   55-7 

4.7  1+4.85 

—       i.i 

3 

I 

Dr.  Gould. 

7    ii.  7 

21 

n   59-8 

4.0J 

-       0.6 

6 

I 

Prof.  Young. 

8      9.0 

18 

12     3-3 

-1-   5-05 

+       0.7 

7 

5 

Mr.  Austin. 

to      8.9 

18 

+    12    13.3 

+       1.6 

8 

3 

Do. 

+   5-44 

The  column  headed  "  irregularity  "  gives  the  deviations  from  a  supposed  uniform 
rate  of  5844,  or  the  additional  correction  required  by  such  a  supposition.  These  are 
mainly  due  to  transportation  of  the  chronometer  to  and  from  the  observatory.  How 
far  they  may  involve  errors  of  observation  will  be  partially  tested  by  comparisons 
with  other  chronometers. 

The  separate  results  for  each  star  observed  on  the  6th  and  7th  of  August  are 
given  in  the  following  table  : 


REPORT  OP  PROFESSOR  COFFIN. 


11 


Meridian  transits,  Burlington,  Iowa. 

Sidereal  chronometer  Hutton  202. 


Date. 

Star. 

No.  of 

wires. 

Chron. 
time. 

Chron.  correction. 

Position  and 
azimuth. 

Observer. 

1869. 

h. 

m.      s. 

Aug.  6 

a     Andromedx    . 

7 

24 

+     11   55-77-      -24A<J 

]                        1 

y     Pegasi  .... 

5 

24 

55.74-      .45Aa 

Clamp  E. 

c     Piscium 

9 

24 

55.42-      .55Aa 

f  a  =  +  i'.3o  f 

Dr.  Gould. 

n     Ursae  Minoris. 

5 

24 

54.9  +30.9   Aa 

J                         J 

7 

o5  Capricorn!. 
K     Capricorn!. 

4 

5 

21 
21 

+     11   59.93—      .83Aa 
59.69—      .goAa 

}   Clamp  E. 

a  =  —  I8.2o 

e     Delphini 

5 

21 

59-95—      -49Aa 

f     Aquarii 

5 

21 

59.83-     .77Aa 

1 

XII  Y.  Cat.,  1879. 

2 

21 

59.92+  3.67AO 

>a  =  -  2'.88 

Prof.  Young. 

XII  Y.  Cat.,  1879. 
6i'Cygni    .... 

2 
2 

21 
21 

59.80+  3.67A* 
59.90—     .o6A0 

)   Clamp  W. 

\  a  =  —  2'.  15 

C    Cygni    .... 

3 

21 

59.72-      .22Aa 

J                         J 

1 

The  observations  of  the  first  three  stars  on  the  7th  are  of  little  value. 

Comparisons  of  the  other  chronometers  with  Hutton  202  were  made  by  coinci- 
dence of  beats  before,  and  of  most  of  them  after,  the  eclipse,  and  on  the  nights  of 
August  6  and  7,  when  they  were  at  distant  stations,  by  means  of  the  electric  telegraph. 
For  this  purpose,  the  chronometers  were  taken  to  the  nearest  telegraph-offices,  and 
signals  passed  at  Burlington  at  each  10"  of  Hutton  202  through  an  entire  minute,  and 
the  times  recorded  by  the  chronometer  at  one  of  the  other  places.  Similar  signals  were 
then  made  at  this  other  station  and  the  times  recorded  by  Hutton  202  at  Burlington- 
Four  or  more  sets  of  such  comparisons,  each  set  comprising  seven  signals,  were  thus 
made  for  each  chronometer. 

The  times  at  Burlington  were  noted  by  Dr.  Gould  and  myself,  and  on  August 
7  also  by  Professor  Young.  The  personal  differences  in  estimating  these  times  were 

C  =  G  —  o8. 1 2  =  Y  —  o9. 1 6. 

The  results  from  each  set  of  seven  comparisons  were  remarkably  uniform. 

CHRONOMETER  CORRECTIONS. 
The  corrections  found  for  the  several  chronometers  are  given  in  the  following  tables  : 


12 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


Corrections  of  chronometer  Negus  i  293. 

Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily 
change. 

Irregu- 
larity. 

Compared  with  Hutton  202  — 

1869.      h. 

h.  m.     s. 

s. 

s. 

July  29  21 

+   5  48  57.7 

—     O-7 

-     0.7 

By  coincidence  of  beats. 

30  21 

57-0 

—      O.  I 

Do. 

Aug.    I  21 

54-4 

1.3 

0.8 

+     0.5 

Do. 

2    21 

53-6 

+     0.5 

Do. 

0.6 

3  21 

53-0 

+     0.3 

Do. 

I  .  I 

4  21 

51.9 

+     0.8 

Do. 

0.5 

5  21 

51-4 

+     0.5 

Do. 

0.05 

7    21 

51-3 

-     0.9 

Do. 

8    21 

50.0 

-     1-3 

-     0.4 

Do. 

•-     0.75 

This  chronometer  was  stationary  except  on  the  7th,  when  it  was  carried  to  Miss 
Mitchell's  station,  half  a  mile  distant. 

Corrections  of  chronometer  Negus  1311. 

Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily  change. 

Irregu- 
larity. 

Compared  with  Hutton  202  — 

1869.      h. 

h.  m.     s. 

s. 

s. 

July  29  21 

+  5  48  52.4 

0.4 

By  coincidence  of  beats. 

30  21 

49-7 

—  2.7 

-     0.3 

Do. 

Aug.    I   21 

43-5 

3-1     * 

+     0.6 

Do. 

2    21 

41.2 

2-3 

+       0.2 

Do. 

3  21 

38.9 

2.3 

—      O.I 

Do. 

4  21 

35-6 

3-3 

+     0.6 

Do. 

6    9 

32.1 

..»! 

+      O.I 

By  telegraph. 

2.1    [—  2.33 

7     9 

30.0 

o    1 

0.4 

Do. 

7  21 

28.6 

2.8J 

-     0.3 

By  coincidence  of  beats. 

8   21 

25.6 

—    3.0 

+      O.I 

Do. 

-    2.63 

August  6  and  7  taken  by  Mr.  Austin  to  Kewanee,  111. ;  on  other  days,  stationary 
in  Burlington. 


REPORT  OF  PROFESSOR  COFFIN. 

Comparisons  by  telegraph. 


13 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.      h. 

h.  m.      s. 

A              A 

Hutton  202  at  Burlington. 

* 

Do. 

31-93 

2 

Monroe 

Burlington  and  Kewanee     . 

Do. 

32.07 

I 

Burlington 

Monroe  and  Kewanee     . 

Negus  1304  at  Monroe. 

Do. 

Negus  1074  at  Monroe. 

31.92 

I 

Burlington 

Monroe  and  Kewanee     . 

Do. 

Kewanee    

Hutton  202  at  Burlington. 

Do. 

29.82 

2 

Monroe 

Burlington  and  Kewanee     . 

Do. 

29.78 

3 

Burlington 

Monroe  and  Kewanee    . 

Negus  1304  at  Monroe. 

29.88 

2 

Monroe 

Kewanee    .      ... 

Negus  1074  at  Monroe. 

Kewanee  is  75  miles  from  Burlington,  on  the  telegraph-line  from  Burlington  to 
Chicago,  and  162  miles  from  Monroe,  Mo.,  on  the  line  from  Chicago  through  Quincy. 
The  latter  line  intersects  the  former  at  Galesburgh,  44  miles  from  Burlington. 

Corrections  of  chronometer  Negus  1304. 


Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily  change. 

Irregu- 
larity. 

Compared  with  Hutton  202  — 

1869.      h. 

h.  m.     s. 

s. 

s. 

July  29    21 

+  5  55  42.2 

o.o 

—     i.i 

By  coincidence  of  beats. 

30     9 

42.2 

o.o 

-     0.9 

Do. 

30    21 

42.2 

—  o.  16 

-     0.7 

Do. 

Aug.  2      9 

41.8 

+    O.2 

-1-       I.O 

Do. 

2     21 

41.9 

0.6 

+     1.2 

By  eye  and  ear.* 

3      9 

42.2 

O.2 

+      I.O 

By  coincidence  of  beats. 

3     21 

42.3 

+     1.2 

Do. 

6      9 

44-9 

1.04") 

o.i    l+o.8c 

—      0.2 

By  telegraph. 

7      9 

45-0 

o  84 

+    0.3 

Do. 

9    21 

47-1 

.  Wlf  J 

-     0.6 

By  coincidence  of  beats. 

to      9 

47-3 

'     1+0.65 

-     0.5 

By  telegraph. 

ii      6 

48.0 

-     0.8 

By  coincidence  of  beats. 

+  0.50 

Taken  by  Mr.  Wiessner  to  Kewanee  between  July  30  and  August  2  ;  to  Monroe 
between  August  4  and  9 ;  and  to  Mount  Pleasant,  Iowa,  between  August  9  and  1 1. 

*  Chronometers  1304  and  1074  were  compared  by  Mr.  Wiessner  with  202  by  noting  an  exact  io»  of  202,  and  with 
each  other  by  noting  an  exact  10'  of  1074,  and  estimating  the  corresponding  second  and  tenths  of  the  other.  Compar- 
ing the  results  with  those  obtained  from  coincidence  of  beats,  I  find  from 

6  comparisons  of  1304  with  202 +  o*.35  ) 

5  comparisons  of  1074  with  202 o*.22  >  +  o«.3o 

9  comparisons  of  1304  with  1074 °'-3i  ) 

to  be  added  to  Mr.  W.'s  estimate  of  the  seconds  and  tenths,  or  subtracted  from  his  estimated  10";  and  accordingly 


14 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 
Comparisons  ly  telegraph. 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.       h. 

h.  m.     s. 

+  e     ce     14    oe 

i 

Burlington       

Do 

7     9 

45.14 

45-01 

+  5  55  45-iS 

dd    8? 

i 
i 

3 

Monroe 
Burlington 

Burlington 

Kewanee    
Monroe  and  Kewanee    . 

Monroe      
Burlington       .... 

Negus  1311  at  Kewanee. 
Do. 

Hutton  202  at  Burlington. 
Do 

10    9 

45-24 

+  5  55  47-20 
4744 

3 
3 

•3 

Burlington 

Burlington 
'Mount  Pleasant 

Monroe  and  Kewanee    . 

Mount  Pleasant  .... 
Burlington       

Negus  1311  at  Kewanee. 

Hutton  202  at  Burlington. 
Do 

Corrections  of  clironometer  Negus  1074. 

Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily  change.  . 

Irregu- 
larity. 

Compared  with  Hutton  202  — 

1869.      h. 

h.  m.     s. 

s. 

s. 

July  29     9 

+  5  56  16.6 

4-   0.70 

—      O.I 

By  eye  and  ear.* 

30    9 

17-3 

+   0.40 

-     °-5 

By  coincidence  of  beats. 

3O  21 

17-5 

-  0.04 

-     0.6 

Do. 

Aug.    2     9 

'7-4 

—    0.2O) 

+     0.3 

Do. 

2   21 

17-3 

o  oo(  -°-°7 

+     0.5 

By  eye  and  ear.* 

3    21 

17.3 

+  0.44  1 

+     0.8 

By  coincidence  of  beats. 

6     9 

18.4 

+  0.50  1+0.62 

+     0.5 

By  telegraph. 

7     9 

18.9 

+  0.84  j 

+     0.3 

Do. 

9  21 

21.0 

—  0.07 

—       I.O 

By  coincidence  of  beats. 

ii     6 

20.9 

-     0.5 

Do. 

+  0.31 

. 

Taken  by  Mr.  Wiessner  to  Kewanee  between  July  30  and  August  2  ;  to  Monroe 
between  August  4  and  9 ;  and  to  Mount  Pleasant  between  August  9  and  1 1 . 

been  subtracted  from  the  chronometer-corrections  derived  from  these  comparisons.  The  accordance  of  the  several  com- 
parisons indicates  uniformity  in  this  personal  peculiarity. 

If  the  error  is  solely  in  estimating  the  seconds  and  tenths,  o'.3o  should  be  subtracted  from  the  corrections  of  1304 
and  1704  and  added  to  the  corrections  of  1311,  obtained  by  telegraph-signals  received  by  Mr.  Wiessner  at  Monroe  on  the 
6th  and  7th  and  Mount  Pleasant  on  the  loth.  If,  however,  the  error  is  solely  in  estimating  an  exact  10',  o".3o  should  be 
added  to  the  corrections  of  130)  and  1374,  obtained  from  telegraph-signals  made  by  him,  and  subtracted  from  the  correc- 
tions of  1311  when  compared  with  1304  or  1374,  provided  he  made  the  signals  exactly  at  the  instant  of  his  estimated  10*. 
The  correction  of  the  telegraph  comparisons  is  therefore  uncertain. 

*See  note  on  pp.  13  and  14. 


REPORT  OF  PROFESSOR  (JOFFIN. 


15 


Comparisons  by  telegraph. 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.      h. 

h.  m.      s. 

Hutton  202  at  Burlington. 

Aug.  6     9 

Do 

TQ     oQ 

18.69 

i 

Burlington 

Monroe  and  Kewance     . 

Do. 
Hutton  202  at  Burlington. 

Aug.    7     9 

19.01 

2 

Monroe 

Kewanee    

Negus  1311  at  Kewanee. 

Corrections  of  chronometer  Negus  1233. 

Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily  change. 

Irregu- 
larity. 

Compared  with— 

1869.        h. 

s 

s. 

s. 

July  29     o 

+62  42.9 

—        I.O) 

+     0.3 

1293,  1304,  1311  by  eye  and  ear. 

29  21 

42.0* 

>  +  0.90 
4-     2.6$ 

+     1.6 

Hutton  202  by  coincidence  of  beats. 

30   21 

44.6 

•  o.o 

0.4 

Do. 

Aug.    i   21 

44.6 

•    0.4 

+     0.6 

Do. 

2    21 

46.2 

+    1.5 

-     0.3 

Do. 

3  21 

47-7 

+     0.3  1 

—     i-5 

Do. 

6     9 

48.4 

—     i.o  I—  0.07 

—     0.8 

Hutton  202  by  telegraph. 

7     9 

47-4 

o.o  J 

+     0.7 

Do. 

7  21 

47-4 

+       I.O 

Hutton  202  by  coincidence  of  beats. 

8    21 

49.1 

—      0.2 

Do. 

+   0.53. 

• 

Taken  by  Professor  Watson  to  Mount  Pleasant  August  4  and  returned  August  7. 

Comparisons  by  telegraph. 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.  h. 
Aug.  6  9 

h.  m.     s. 
+    6  2  48.63 

i 

i 

Burlfngton  . 

Mount  Pleasant    .... 

Hutton  202  at  Burlington. 
Do. 

48.26 
48.51 

i 
i 

Ottumwa 
Burlington  . 

Burlington  and  Mt.  Pleasant 
Mt.  Pleasant  and  Ottumwa. 

Do. 
Daniels    -§-  at  Ottumwa. 
Do8'5 

Aug.  7  9 

48.65 
+62  47.51 

i 

3 
2 

Ottumwa 
Burlington  . 

Mount  Pleasant    .  •    . 
Mount  Pleasant   .... 

Do. 

Hutton  202  at  Burlington. 
Do, 

47.28 
47-40 
47.38 

2 

3 

2 

Ottumwa 
Burlington  . 
Ottumwa     . 

Burlington  and  Mt.  Pleasant 
Mt.  Pleasant  and  Ottumwa. 
Mount  Pleasant    .... 

Do. 
Daniels  -5-  at  Ottumw'a. 
Do"5 

*  Probably  an  error  of  I"  in  the  comparison,  one  only  having  been  made. 


16 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


Mount  Pleasant  is  on  the  telegraph-line  of  the  Burlington  and  Missouri  River 
Railway,  28  miles  from  Burlington ;  Ottumwa  is  on  the  same  line,  75  miles  from  Bur- 
lington. 

Corrections  of  sidereal  chronometer  Negus  578. 

Referred  to  sidereal  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chron. 
time. 

Chronometer 
correction. 

Daily 
change. 

Irregu- 
larity. 

Compared  with  — 

1869.          h. 

h. 

m.      s. 

s. 

s. 

Aug.   3  21.8 

7 

-     31  24.4 

-     3.76 

—      O.2 

Negus  1293  by  coincidence  of  beats. 

6    9.9 

!9 

33.8 

4-33 

+      0.4 

Hutton  202  by  telegraph. 

7  21.9 

7 

40.3 

—      O.2 

Negus  1311  by  coincidence  of  beats. 

-     3-98 

Taken  by  Professor  Watson  to  Mount  Pleasant  August  4  and  returned  August  7. 

Comparisons  by  telegraph. 


Burlington 
mean  time. 

Chron. 

time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.  h. 
Aug.  6  9 

h. 
19 

m.      s. 
-     31  33-57 
34.02 

I 

2 

Burlington 
Mount  Pleasant 

Mount  Pleasant  .... 
Burlington      

Hutton  202,  Burlington. 
Do. 

33-74 

2 

Ottumwa    . 

Burlington  and  Mt.  Pleasant 

Do. 

33.48 

I3.fl      Q7 

I 

2 

Burlington 

Ottumwa  and  Mt.  Pleasant. 

Daniels  ^-,  at  Ottumwa. 
815' 

Do 

33-55 

2 

Ottumwa    . 

Mount  Pleasant   .... 

Do. 

Corrections  of  chronometer  Daniels  gy> 

Referred  to  mean  time  of  Burlington  C.  S.  station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily 
change. 

Irregu- 
larity. 

Obtained  from  — 

1869.      h. 

h.  m.    s. 

s. 

s. 

Aug.  I      21 

+     5  57   1-2 

—  0.4 

+    0.2 

Comparison  with  Hutton  2O2*by  coincidence  of  beats. 

3      ° 

0.9 

+   1.8 

A.  M.  and  P.  M.  observations  of  sun  at  Ottumwa. 

+  3-4 

4      0 

4-2 

-  0.6 

Do. 

+  i  .0 

6      o 

6.5 

+  1.9 

-  0.6 

Comparison  with  Hutton'2O2  by  telegraph. 

6     22 

7-5 

-    1-5 

A.  M.  observations  of  sun  at  Ottumwa. 

—  2.2 

7      9 

6.4 

+  1.2 

+  0.5 

Comparison  withi  Hutton  202  by  telegraph. 

9      o 

8.3 

+  0.3 

A.  M.  andT.'M.  observations'ofjsun  at  Ottumwa. 

+  0.98 

Taken  by  Professor  Alexander,  August  2,  to  Ottumwa,  on  the  line  of  the  Bur- 
lington and  Missouri  River  Railway,  75  miles  from  Burlington.     Professor  Alexan- 


BEPORT  OF  PROFESSOR  COFFIN. 


17 


der's  observations  for  time  at  Ottumwa  are  described  at  the  end  of  his  report.  They 
were  reduced  to  Burlington  time  by  adding  the  assumed  difference  of  longitude,  5™ 
6\7. 

Comparisons  by  telegraph. 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals  made  at 

Received  at 

Compared  with 

1869.        h. 

h.  m.     s. 

_l_   -c    CT  6   cfi 

Hutton  202  at  Burlington. 

.26 

^ 

Ottumwa 

Burlington     

Do. 

.70 

•  43 
.27 

3 
I 
I 

Mount  Pleasant 
Burlington 
Ottumwa    . 

Burlington  and  Ottumwa  . 
Mount  Pleasant  and  Ottumwa 
Mount  Pleasant        .... 

Do. 
Negus  1233,  at  Mount  Pleasant. 
Do. 

.85 

I 

Mount  Pleasant 

Do. 

.21 
.26 

2 
2 

Burlington 
Ottumwa    . 

Mount  Pleasant  and  Ottumwa 
Mount  Pleasant  

Negus  578,  at  Mount  Pleasant. 
Do 

.70 
-1-   c   <;7  6.  =;"* 

I 

•3 

Mount  Pleasant 

Ottumwa  
Ottumwa  

Do. 
Hutton  202,  at  Burlington. 

•31 

2 

Do 

.41 

3 

2 

Burlington 

Mount  Pleasant  and  Ottumwa 

Negus  1233,  at  Mount  Pleasant. 
Do 

Corrections  of  chronometer  Negus  2335. 

Referred  to  mean  time  of  Burlington  C.  S/ station. 


Burlington 
mean  time. 

Chronometer 
correction. 

Daily 
change. 

c-o 

Compared  with  — 

1869.        h. 

h.  m.      s. 

s. 

s. 

Aug.  I      21 

-H   5   55   56.8 

—  0.2 

Hutton  202  by  coincidence  of  beats. 

i  -H  1.9 

4     12 

56     1.8          :  6 

+  0.4 

Daniels  —  -  by  eye  and  ear. 

5      12? 

3.4 

.       +0.5 
4.0 

Do. 

6      o? 

5-7 

—  I.O 

Do. 

O.O      I 

7      9 

6.8 

0.0 

Hutton  202  by  telegraph. 

O.7 

9      o 

7-9 

0.8 

+  0.4 

Daniels  /-  by  eye  and  ear. 

015 

10        0 

8-7 

0.0 

Do. 

[+  1.47    -  o.24(/-6")] 

Taken  to  Ottumwa  August  2,  by   Professor  Alexander.     The  times  when  the 
comparisons  were  made,  on  August  5  and  6,  are  doubtful. 

Comparisons  by  telegraph 


Burlington 
mean  time. 

Chronometer 
correction. 

No.  of 
sets. 

Signals 
made    at 

Received  at 

Compared  with 

1869.       h. 

h.  m.     s. 

Aug.    7     9 

+  5  56  7-n 

2 

Burlington  . 

Ottumwa 

Hutton  202,  at  Burlington. 

6.51 

2 

Ottumwa 

Burlington  . 

Do. 

3  E  S 


18 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


The  last  column  in  the  table  for  each  chronometer  gives  the  corrections  which 
would  be  required  by  the  supposition  that  its  rate  was  uniform  and  that  these  irreg- 
ularities arose  from  errors  in  the  determination  of  the  chronometer-corrections.  When 
they  are  collected,  however,  as  in  the  following  table,  we  see  that  the  mean,  on  each 
date,  for  several  chronometers  is  small,  and  hence  indicative  that  those  for  Hutton  202, 
on  which  the  others  depend,  are  mainly  irregularities  in  its  motion,  and  but  little  due 
to  errors  of  observation. 


Burlington 
mean  time. 

Hutton  202. 

C«1 

O* 
« 

M 
• 

i 

• 

z 

en 

»-i 

OB 

M 

<u 

Z 

o 

en 

(/) 

3 

em 

o> 

Z 

-r 
r^ 

o 

V) 

EC 

O 

Z 

en 
m 
n 

M 
3 

Eg 

V 

Z 

CO 

r^ 
in 

BO 

3 

bo 

V 

Z 

ui 

C*) 

m 
w 
c/] 

3 

C>0 

y 

Z 

Daniels  ±. 

c 
• 
o 

s 

No.  of  chro- 
nometers. 

1869.       h. 
July  29   21 

s. 
+     0.6 

s. 
-     0.6 

s. 

•    0.4 

s. 
—     i.i 

s. 

—      O.I 

s. 
+     1.6 

s. 

s. 

s. 

s. 
o.o 

6 

30     9 

+     0.6 

.    . 

.  . 

-     0.9 

-     0.5 

.    . 

-  0.3 

3 

21 

-1-     0.6 

-     0.6 

-     0.3 

-     0.7 

-     0.6 

-     0.4 

•  • 

•    • 

-  0.3 

6 

Aug.    I     21 

+     0.4 

+     0.5 

-t-     0.6 

-t-     0.6 

.     . 

—    O.2 

+    0.2 

+  0.3 

6 

2      9 

+     0.3 

H-      1.0 

+     0.3 

.  . 

.     . 

.     . 

+  0.5 

3 

21 

-     0.3 

+     0.5 

+      O.2 

+       1.2 

+     0.5 

-     0.3 

."  . 

.     . 

+  0.3 

6 

3     9 

-     0.9 

+       1.0 

.    . 

.    . 

.     . 

o.o 

2 

21 

-     1-3 

+     0.3 

—      O.I 

+       1.2 

+     0.8 

-     1-5 

—       0.2 

.     . 

—    O.I 

7 

4   21 

i-4 

+     0.8 

+     0.6 

.     . 

.    . 

.     . 

o.o 

3 

5   21 

—      1.2 

+     0.5 

.    . 

-  0.8 

2 

6     9 

—      I.I 

•    • 

+      O.I 

+      0.2 

+     0.5 

-     0.8 

+      0.4 

.     . 

—    1-5 

-  0.3 

8 

7     9 

-     0.7 

•    • 

-     0.4 

+      0.3 

+     0.3 

+     0.7 

o.o 

+  0.5 

o.o 

7 

21 

—      O.I 

-     0.9 

-     0.3 

+       I.O 

—      O.2 

.   . 

—    O.I 

5 

8     21 

+    0.9 

-     0.4 

+       O.I 

.     . 

—      O.2 

.    . 

4    o.l 

6 

9   21 

+       1.2 

.    . 

.    . 

-     0.6 

—       I.O 

—    O.I 

3 

IO     9 

+     1.6 

-     0.5 

-     0.5 

•     • 

-t-    0.2 

3 

THE    ECLIPSE-STATION,    BURLINGTON. 

A  vacant  square,  between  7th  and  8th  streets  on  the  east  and  west,  and  Elm  and 
Maple  streets  on  the  north  and  south,  was  selected  as  a  suitable  place  for  observations 
of  the  eclipse.  It  is  in  the  vicinity  of  the  Coast  Survey  station  and  on  the  summit  of 
the  same  hill,  in  a  quiet  location,  surrounded  by  a  hedge,  and  free  from  dust.  My 
request  for  its  use  was  cordially  granted  by  its  proprietor,  H.  W.  Storr,  Esq. 

It  is  elevated  1 56  feet  above  high-water  mark  of  the  Mississippi  River  at  Bur- 
lington, and  about  630  feet  above  the  ocean.  Beyond  its  limits,  the  ground  slopes 
abruptly  to  the  river  on  the  east  and  a  ravine  on  the  north,  but  more  gently  to  the 
west  and  south. 

A  temporary  observatory  was  erected  near  the  middle  of  this  lot,  16  feet 
square,  with  a  small  addition  5  feet  square  at  the  northeast  corner.  It  contained  two 
suitable  dark  rooms  for  the  photographers,  and  afforded  shelter  for  other  instruments 
as  well  as  the  equatorial  of  the  Philadelphia  High  School,  for  which  it  was  specially 
designed. 

The  roof,  sloping  east  and  west,  was  mainly  of  roofing-paper  on  light  sliding 


REPORT  OF  PROFESSOR  COFFIN.  \&*   ify^ 


T4, 


frames.     Though  exposed  to  a  severe  storm,  it  was  uninjured  by  the  heavy  wi 
proved  impervious  to  the  rain. 

A  cross  of  8-inch  timber  was  laid  to  support  the  equatorial,  and  a  meridian  line 
transferred  from  the  meridian  line  of  the  Coast  Survey  station,  which  had  been  pre- 
viously marked,  was  traced  on  it  by  Mr.  Austin-  and  the  city  surveyor,  Mr.  Ham. 
From  their  measurements,  the  position  of  the  equatorial  was  found  to  be  S.  25° 
22'  W.,  296  feet,  or  2". 6  south  and  oa.  11  west,  from  the  Coast  Survey  station,  or  in 
latitude  40°  48'  20". 5  north,  and  longitude  oh  56  i3".84  zr  14°  3'  2 7". 6  west  of 
Washington; 

Previous  to  my  arrival,  the  city  council  of  Burlington  appointed  the  mayor,  Hon. 
William  Bell,  and  Aldermen  G.  W.  E.  Edwards,  B.  Y.  Overtoil,  and  Charles  O'Brien 
a  committee  "  with  full  power  to  extend  all  needed  facilities  to  those  who  should  visit 
the  city  to  take  observations  of  the  eclipse."  Besides  other  considerate  attentions, 
they  provided  a  special  police  officer,  to  giiard  the  observatory  at  night ;  and  their 
presence,  with  several  city  officers,  at  the  time  of  the  eclipse,  was  sufficient  to  prevent 
the  pressure  of  a  crowd,  and  to  secure  for  us  the  quiet  and  freedom  from  interruption 
or  distraction  which  were  essential  to  the  success  of  our  observations. 

PREPARATIONS    FOR   THE    ECLIPSE. 

At  noon  of  Wednesday,  the  4th  of  August,  all  the  parties  and  instruments  had 
arrived ;  but  little,  however,  could  be  done  toward  mounting  the  large  telescope  until 
the  next  day,  when  it  was  successfully  accomplished.  It  was  adjusted  nearly  in  posi- 
tion by  Professor  Mayer,  by  the  method  described  in  his  report,  without  stars,  and 
with  the  aid  only  of  a  plumb-line  and  the  meridian-line,  which  had  been  previously 
traced.  The  subsequent  work  of  completing  the  adjustment  more  closely  by  stars 
was  very  slight. 

The  weather  for  several  days  had  been  pleasant,  but  the  atmosphere  had  now 
become  thick  and  smoky,  with  appearances  of  an  approaching  storm  ;  and  the  night 
of  the  th  set  in  cloudy,  with  our  preparations  incomplete,  and  instruments  only  par- 
tially adjusted.  The  6th,  the  day  before  the  eclipse,  was  rainy,  with  a  blustering 
northeast  wind,  and  indications  of  a  long  continuance  of  bad  weather. 

But  notwithstanding  such  unpromising  prospects,  preparations  were  continued 
so  far  as  was  practicable ;  and  at  night,  the  chronometers  at  the  several  stations  were 
compared  by  telegraph,  as  had  been  previously  arranged.  Soon  after  midnight,  how- 
ever, the  clouds  began  to  break ;  and  at  2  a.  m.  of  the  ;th,  Dr.  Gould  and  Professor 
Mayer  accompanied  me  to  South  Hill  to  obtain  more  observations  for  time,  and 
complete  the  adjustments  of  their  instruments.  Clouds  still  interfered,  and  the  work 
was  barely  accomplished  when  daylight  interrupted  it. 

By  10  a.  m.  of  the  /th,  clouds  had  entirely  disappeared,  the  wind  was  moderate 
from  southeast,  and  the  atmosphere  remarkably  clear.  It  continued  thus  bright  and 
pleasant  through  the  day.  Preparations  were  completed,  though  in  some  respects 
hurriedly  and  not  altogether  satisfactorily. 


20  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

ARRANGEMENT   OF    THE    PARTY. 

Professor  Young,  Professor  Mayer,  and  the  photographic  party  were  stationed 
within  the  observatory  ;  Dr.  Gould  and  myself  outside,  about  twenty  feet  to  the  west. 
Near  the  southwest  corner,  outside,  was  placed  a  Dolland  telescope  of  i\  inches  aper- 
ture, which  Professor  Young  had  provided.  His  assistant,  Mr.  Emmerson,  fitted  it 
with  a  screen  of  white  Bristol-board,  on  which  was  thrown  an  image  of  the  sun, 
enlarged  by  the  eye-piece  to  a  diametev  of  about  six  inches.  Dr.  Gould,  Professor 
Eaton,  of  Brooklyn,  N.  Y.,  Mr.  Stockwell,  of  Ohio,  and  others,  observed  the  contacts 
with  it. 

Rev.  J.  Freeman  Clarke,  of  Boston,  with  a  party  of  friends  and  a  Clark  telescope 
of  4  inches  aperture,  was  a  little  farther  '-emoved  to  the  west. 

Miss  Mitchell's  party  was  in  another  part  of  this  city,  in  the  grounds  of  the  Bur- 
lington Collegiate  Institute,  north  and  west  from  the  Coast  Survey  station. 

The  sidereal  chronometer  Hutton  202  was  placed  just  outside  of  the  door,  on 
the  west  side  of  the  observatory.  The  seconds  were  counted  audibly,  in  a  clear  voice, 
by  Mr.  Miles  Rock,  C.  E.,  of  Bethlehem,  Pa.,  and  tapped  with  an  observing-key  for 
record  on  the  Morse  register-chronograph  of  the  Washington  Observatory,  within  the 
building.  Mr.  Otis  Kendall,  of  Philadelphia,  was  stationed  at  the  chronograph,  to  call 
the  minutes  and  note  them,  and,  occasionally,  the  seconds  on  the  fillet.  They  were 
relieved  in  these  labors  several  times,  respectively,  by  Mr.  J.  Bonsai  and  Mr.  Charles 
Stoddard,  of  Burlington.  This  work  was  performed  with  commendable  fidelity. 

From  the  table,  page  10,  we  have  for  the  correction  of  this  chronometer  during 
the  period  of  the  eclipse, 

+  IIm  588.05+08.20  (t  —  I2h) 

to  local  sidereal  time  of  the  Coast  Survey  station ;  and 

+  i5h6mi69.7o-98.63  (£-i2h) 
as  the  reduction  to  local  mean  time,  t  being  the  time  by  chronometer  in  hours. 

# 

METEOROLOGICAL    OBSERVATIONS. 

The  observatory  on  South  Hill  was  provided  with  only  a  pair  of  Fahrenheit 
thermometers,  made  by  Mr.  James  Green,  of  New  York,  one  of  them  arranged  for  a 
wet  bulb,  and  an  aneroid  barometer,  which  was  compared  by  Mr.  Green  with  his 
standard  in  New  York  before  and  after  the  eclipse,  and  found  to  be  correct.  These 
were  supplied  by  Mr.  Green,  as  also  a  standard  mercurial  barometer,  which,  however, 
was  deranged  in  transportation,  and  rendered  useless.  Other  desirable  instruments  I 
was  unable  to  obtain. 

The  aneroid  and  thermometers  were  exposed  to  a  free  circulation  of  air  on  the 
east  side  of  the  observatory  near  the  northeast  corner,  but  sheltered  from  the  wind 
and  sun. 

Mr.  H.  Thielson,  engineer  of  the  Burlington  and  Missouri  Railway,  was  provided 
with  similar  instruments  and  kept  a  record  of  thqm  during  the  afternoon  of  the  eclipse 
at  his  house  about  half  a  mile  N.NE.  from  the  observatory,  and  70  feet  lower.  His 
readings  of  the  aneroid  barometer  have  been  diminished  by  0.46  inch,  the  correc- 
tion obtained  by  comparisons  with  the  other  instrument  on  several  different  lays. 


KEPOET  OF  PBOFESSOB  COFFIN. 

Burlington,  August  7,  1869. 


21 


Burlington 
mean  time. 

On  South  Hill. 

At  Mr.  Thielson's 

Remarks. 

Aneroid 
barom. 

Thermom's  — 

Wind. 

\neroid 
barom. 

Thermometers  — 

Dry. 

Wet 
bulb. 

At. 

Dry. 

Wet 

bulb. 

h,  m. 

in. 

• 

• 

Southeas  erly  ;  light 

in. 
29.68 
29.68 
29.68 
29.67 
29.66 
29.66 

29.65 
29.64 
29.63 
29.63 

77-9 
79.0 
79.0 
79.8 

79-9 
80.0 

79-9 
79-4 
76.7 
75-0 

74-4 

74-4 
75-5 
74.8 
75-2 
74-5 

74-2 
74.0 
70.0 
69.2 
68.0 

65.2 
65.2 
66.5 

65.3 
66.3 
66.0 

65.0 
65.0 
62.0 
62.0 
62.0 

Eclipse  began. 
Eclipse  total. 

Eclipse  ended. 

I   30 

2      O 

2  30 
3     o 
3  30 
3  40 
4     o 
4  20 
4  40 
4  5° 
4  55 
5     o 
5     2 
5   10 
5  20 
5  30 
5  40 
6     o 
6  20 

29.70 

71.2 

29.66 
29.64 
29.62 
29.63 
29.61 

70.8 
71.2 
70.0 
69.2 
67.5 

60.0 
61.2 
60.0 
60.0 

58.3 

Southeasterly  ;  light 

66.0 

29.62 
29.61 
29.61 
29.61 
29.61 
29.61 

74.0 

72.5 
72.0 
71.0- 
71.2 
71.6 

67.0 
67.2 

67.7 
68.8 
69.0 
68.0 

62.0 
62.0 
62.8 
63.0 
63.0 
63.0 

29.59 

66.2 

59.0 

Southeasterly;  very  light 

29.58 
29.58 
29.58 

66.8 
67.0 

65.8 

60.0 

59-7 
59-5 

Southeasterly;  light 

The  sky  generally  appeared  perfectly  clear ;  but  at  4*  34m  p.  m.,  Mr.  Rock  noted 
a  "low  bank  of  clouds  in  western  horizon."  Mr.  Gr.  C.  Morton,  of  Burlington,  who, 
with  others,  was  watching  the  eclipse  on  an  eminence  in  the  northern  part  of  the  city 
of  Burlington,  states  that  none  of  the  party  "had  noticed  a  cloud  in  the  sky  before 
the  eclipse;  we  all  spoke  of  the  perfectly  clear  atmosphere,  there  being,  seemingly, 
absolutely  nothing  to  prevent  full,  unobstructed  view  in  every  direction.  Yet  when 
the  totality  came,  clouds  extending  along  the  horizon  to  the  north  were  very  plainly 
to  be  seen.  Some  one  called  my  attention  to  the  beautiful  appearance  of  a  bank  of 
clouds  near  the  horizon  at  a  particularly  fortunate  moment.  At  the  instant  I  turned,  the 
moon's  shadow  was  very  clearly  denned  on  the  top  of  the  bank,  giving  a  remarkably 
happy  effect  with  the  bright  sunlight  on  that  side  farthest  from  me,  and  the  dark 
shadow  on  the  other."  Clouds  invisible  in  full  sunlight,  appear  to  have  been  noticed 
by  others  several  minutes  before  the  total  obscuration. 

OBSERVATIONS    OF    THE    ECLIPSE. 

I  used  for  observing  the  eclipse  a  telescope  made  by  Alvan  Clark  &  Sons, 
adjustable  for  latitude,  with  3  inches  aperture,  48  inches  focal  length,  and  magnifying 
power  of  3 1  ;  a  diagonal  eye-piece  adapted  especially  for  observations  of  the  sun,  the 
reflector  being  simply  a  plate  of  glass,  inclined  45°  to  the  optical  axis  of  the  telescope, 


22  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

and  reflecting  only  about  one-half  of  the  rays  to  the  eye  ;  it  was,  therefore,  equivalent 
to  a  diminution  of  the  aperture  to  2.1  inches.  The  telescope  was  furnished  with  three 
shade-glasses,  of  one,  two,  three  thicknesses,  respectively,  of  glass  of  that  peculiar 
neutral  tint  called  London  smoke.  The  deepest  of  these  presented  a  pleasant,  softened 
image  of  the  full  sun,  and  was  used  at  the  beginning  and  end  of  the  eclipse;  the 
lightest  was  used  at  the  commencement  and  during  the  first  part  of  the  total  obscura- 
tion. The  field  of  view  was  62'  in  diameter,  or  double  the  apparent  diameter  of  the 
sun,  and  was  divided  into  octants  by  four  spider-lines  in  the  focus  of  the  eye-lens. 
There  was  nothing,  however,  to  distinguish  the  lines,  or  to  measure  the  rotation  of  the 
diaphragm;  and  its  connection  with  a  diagonal  eye-piece,  which  presents  neither  a 
direct  nor  inverted,  but  a  reversed  image,  and  coidd  be  rotated -about  the  axis  of 
either  the  telescope  or  the  eye-tube,  added  to  the  difficulty  of  estimating  angles  of 
position  with  any  precision  or  certainty. 


FIRST  CONTACT. 


I  noted  the  first  contact  at  1 2h  50™  4"  by  the  chronometer,  or  3''  56™  1 2".  5  mean  time 
of  the  Eclipse  Station.  There  was  nothing  to  indicate  the  approach  of  the  moon 
before  actual  indentation  of  the  sun's  limb.  This  time,  therefore,  may  be  too  late  by 
2s  or  3",  but  would  not  be  too  early. 

NOTES    OF    THE   ECLIPSE. 

• 

The  definition  of  the  telescope  was  excellent;  and  during  the  eclipse,  the  limb  of 
the  sun  appeared  smooth  and  well  defined.  The  moon's  limb,  however,  appeared  in 
some  portions  slightly  serrated.  This  was  especially  noticeable  in  the  eastern  limb 
soon  after  the  beginning  of  the  eclipse:  but  the  magnifying  power  was  insufficient  for 
the  detection  of  any  particular  prominences  or  depressions.  This  irregular,  serrated 
appearance  was  specially  noted  near  the  southern  cusp  at  4h  i™  local  mean  time,  and 
about  one-third  the  distance  from  the  southern  to  the  northern  cusp  at  4h  36'".  The 
cusps,  during  the  greater  portion  of  the  eclipse,  were  very  sharply  defined.  Irregu- 
larities were  occasionally  noticed,  and  the  following  noted :  At  4''  53™,  the  southern 
cusp  appeared  blunted  and  irregular,  but  soon  after  resumed  its  sharp  appearance. 
After  the  total  obscuration,  at  5h  im  40",  the  southern  cusp  was  terminated  by  a 
detached  luminoiis  point.  At  5''  3^"  and  5b  2im,  the  northern  cusp  appeared  blunted 
and  irregular. 

About  7'"  after  the  total  obscuration,  a  narrow  band  sensibly  brighter  than  the 
rest  of  the  solar  crescent,  seemed  to  skirt  the  moon's  limb.  This  was  the  only  time 
that  I  noticed  this  appearance.  The  lightest  shade-glass  was  on  at  the  time. 

The  largest  and  most  fully  developed  solar  spot  was  in  the  southwest  quadrant 
of  the  sun's  disk.  The  first  contact  of  the  moon's  limb  with  the  edge  of  its  nucleus 
was  noted  at  i3b  I4m  52"  by  chronometer,  or  4''  20™  56".6  local  mean  time;  the  entire 
disappearance  of  the  nucleus  at  i3h  i6m  27",  or  4''  2 2'"  31  ".3  local  mean  time  (probably 
im  too  great,)  and  its  completed  re-appearance  at  14''  9'"  20",  or  5h  15'"  i68  local  mean 
time.  The  "outlines,  both  of  the  penumbra  and  nucleus,  of  this  spot  were  very 


REPORT  OF  PROFESSOR  COFFIN.  23 

• 

irregular.     Other  spots  were  visible;  but,  excep"  a  large  one  near  the  sun's  eastern 
limb,  they  were  quite  small  and  hardly  distinguishable  when  close  to  the  moon's  limb. 


THE    TOTAL    OBSCURATION. 

For  two  minutes  before  the  total  disappearance  of  the  sun,  the  lightest  shade 
glass  was  sufficient  to  protect  the  eye.  The  visible  portion  of  the  sun  was  reduced  to 
a  very  narrow  crescent,  sharply  and  beautifully  denned,  with  hardly  perceptible 
irregularities,  and  sensibly  diminishing  in  breadth  and  extent.  When  reduced  to  a 
slender  thread  of  light  about  30°  or  40°  of  the  sun's  limb  in  extent,  it  seemed 
suddenly  to  break  into  distinct  portions,  to  elongate  in  both  directions,  and  then  shorten 
and  run  together  with  great  rapidity — changing  so  quickly  that  any  distinction  of 
portions  or  of  separating  lines  could  not  be  noted;  and  then  rapidly,  but  not  instan- 
taneously, to  disappear.  Except  the  illusory  appearance  of  elongation,  the  phenomena 
were  simply  such  as  would  result  from  the  serrt.ted  irregularities  of  the  moon's  limb. 

The  time  of  total  disappearance  was  noted  at  13''  51'"  46"  by  chronometer,  or 
4h  57™  44"- 6  local  mean  time. 

THE    CORONA. 

At  the  instant  of  the  sun's  disappearance,  the  corona  flashed  out  with  unexpected 
brightness,  shining  with  a  soft,  nebulous,  silvery-white  light,  with,  perhaps,  a  slightly 
bluish  tinge  as  seen  through  the  shade-glass.  It  was  more  brilliant,  seemingly  of 
greater  density  close  to  the  moon,  fading  away  to  indistinctness  in  all  directions.  It 
was  unequally  distributed,  and  could  be  traced  in  some  directions  to  a  greater  distance 
than  in  others.  Its  structure  was  radial,  but  not  distinctly  striated. 

In  the  direction  20°  south  of  the  place  of  the  sun's  disappearance,  as  estimated  at 
the  time,  or  about  117°,  reckoned  from  the  north  point  of  the  moon's  disk,  toward  the 
east,  the  corona  was  cut  off  by  the  limit  of  the  field  of  view,  the  moon  being  a  little  out 
of  the  center  in  that  direction.  In  nearly  the  opposite  direction,  it  could  be  distinctly 
traced  to  the  limit  of  the  field.  Thus  its  entire  extent  as  far  as  visible,  was 
fully  64'.  It  could  be  traced  nearly  to  the  limit  of  the  field  towards  the  south-south- 
east and  southwest ;  but  its  extent  in  other  directions  was  more  limited,  and,  at  right 
angles  to  the  greatest  elongation,  was  only  two-thirds  the  breadth  of  the  field,  or  41'. 

Plate  I,  Figure  i,  represents  nearly  its  appaient  outline  in  the  field  of  the  tele- 
scope. The  two  radial  points  in  the  south-southeast  and  southwest  directions  were, 
however,  more  distinctly  marked,  and  the  small  portion  of  visible  sky  darker  than  is 
represented. 

The  greatest  elongation  was  also  estimated  to  be  in  the  direction  5°  north  of  the 
prominence  hereafter  described  as  the  first  which  was  noticed.  This  direction  will  be 
92°  or  105°,  reckoned  from  the  north  point  of  the  disk,  as  we  regard  this  prominence 
as  identical  with  No.  4  of  Professor  Mayer's  diagram,  Plate  X,  figure  1,  as  seems  most 
probable,  or  with  No.  5.  Neither  differs  greatly  from  107°. 2,  the  position  of  the 
ecliptic,  or  103°. 7,  the  intersection  of  the  plane  of  the  sun's  equator  with  that  of  the 
sun's  disk.  The  position  of  the  sun's  axis  at  the  time  of  the  eclipse  was  13°. 7,  the 


24  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

north  pole  being  6°.4  of  a  meridian  circle  of  the  sun  within  the  disk,  or  the  sun's 
equator  passing  6°. 4  south  of  the  center. 

The  elongation  of  the  corona  in  the  direction  of  the  equator  is  manifest  in  Dr. 
Gould's  diagrams,  Plate  II ;  but  it  is  equally  so  in  the  direction  of  the  axis  ;  while  in 
mine  the  minimum  breadth  is  in  that  direction. 

In  comparing  such  representations,  it  should  be  considered  that  here  the  view  was 
with  a  telescope  of  diminished  aperture  and  through  a  light  shade-glass,  and  that  dif- 
ferent persons  will  estimate  differently  the  distance  to  which  they  may  be  able  to  trace 
a  fading  light  until  it  becomes  invisible  ;  and  even  the  same  person  may  estimate  such 
distance  differently  in  different  directions  or  in  different  planes  through  the  axis  of 
the  eye.  In  the  present  case,  this  last  point  could  have  been  readily  tested  by  simply 
rotating  the  diagonal  eye-piece,  and  thus  changing  the  position  of  the  image  in  the 
field  of  view  with  reference  to  the  eye  of  the  observer. 

The  light  of  the  corona  reminded  me  at  the  time  of  colorless  streamers  of  the 
aurora  borealis,  as  sometimes  seen,  and  subsequently  of  the  nebula  of  Orion,  as  seen 
through  a  large  telescope;  and  the  tail  of  the  great  comet  of  1843,  as  seen  with  the 
naked  eye.  Indeed,  a  similarity  in  composition  with  the  tails  of  comets  is  not  improb- 
able. 

THE   PROMINENCES. 

Simultaneously  with  the  sun's  disappearance,  a  large  prominence  appeared  sud- 
denly to  shoot  up  from  the  eastern  limb  of  the  moon,  pyramidal  in  shape,  but  rounded 
at  the  top,  and  its  outline  broken  and  irregular.  It  appeared  to  me  of  a  beautiful  rose- 
color,  very  soft  and  delicate,  more  deeply  tinted  at  the  top  than  at  the  base,  and  to 
stand  out  in  bold  relief  from  the  white  corona,  which  apparently  formed  the  back- 
ground. Its  altitude  was  estimated  to  be  2l'  or  3',  its  base  10°  of  the  moon's  limb, 
and  its  position  20°  to  30°  south  of  the  place  of  the  sun's  disappearance,  or  117° 
to  127°  from  the  north  point  of  the  disk.  It  is  probably  identical  with  No.  4  of  Pro 
fessor  Mayer's  description  of  the  photographs,  whoso  position  is  96°,  but  may  be  No. 
5,  in  position  110°.  The  "eagle-wings"  of  No.  4,  which  appears  to  have  attracted 
the  attention  of  most  observers,  as  other  prominences  on  the  eastern  limb,  may  have 
been  obscured  by  the  colored  glass  until  they  were  too  faint  to  be  noticed. 

Another  prominence,  similar  in  shape  and  color,  but  larger,  appeared  as  suddenly 
and  almost  simultaneously  on  the  southwest  limb,  extending  about  13°  along  the 
moon's  limb,  and  rising  to  an  altitude  of  3'.  Its  estimated  distance  from  the  one  first 
described  was  120°,  and  its  position  237°  to  247°,  which  identifies  it  with  No.  8  of 
Professor  Mayer's  description,  whose  position  on  the  photographs  is  238°.  This  is  the 
large  prominence  on  the  moon's  lower  limb  which,  more  than  any  other,  attracted  the 
notice  of  spectators. 

It  was  followed  soon  after  by  two  others  of  the  northwest  limb,  one  similar  in 
shape  and  color  to  the  two  already  described,  but  smaller,  and  estimated  about  95°  or 
1 00°  from  the  last.  It  is  probably  No.  1 1  of  Professor  Mayer's  diagram,  in  position 
318°.  The  other,  about  25°  west  of  it,  appeared  in  shape  like  a  large  mushroom,  the 
stem  of  a  pale  light,  surmounted  by  a  large  head  of  the  same  beautiful  rose  color  as 

See  Professor  Mayer's  report,  and  Plate  X,  figure  1. 


REPORT  OF  PROFESSOR  COFFIN.  25 

the  other  prominences,  extending  about  5°  of  the  moon's  limb.     It  is  designated  as 
No.  10,  in  position  288°.     The  altitude  of  each  of  these  two  was  estimated  at  i'  to  i£'. 

Connecting  them,  and  extending  westward  beyond  the  last  about  20°  or  25° 
toward  the  large  prominence,  was  a  band  of  rose-colored  light,  closely  skirting  the 
moon's  limb,  and  not  more  than  i'  in  altitude.  This,  as  well  as  the  prominences, 
appeared  to  stand  out  in  bold  relief  from  the  corona. 

On  removing  the  shade-glass,  about  one  minute  after  the  sun's  disappearance,  the 
whole  scene  greatly  increased  in  brilliancy.  The  corona  near  the  moon's  limb  now 
shone  with  a  glistening  light,  like  the  glow  from  a  surface  of  molten  metal  in  a  fur- 
nace, and  extended  throughout  the  field,  so  that  no  outline  could  be  distinguished. 

The  prominences  presented  the  same  beautiful  hue,  but  brighter  and  more  intense. 
That  on  the  eastern  limb  appeared  smaller,  and  gradually  faded  away.  The  large 
one  on  the  southwest  limb  appeared  the  same  in  size  and  shape.  Those  in  the  north- 
west appeared  larger,  and  the  corona  in  that  direction  seemed  to  brighten  as  the  total- 
ity approached  its  termination. 

The  prominences  seemed  constantly  to  occupy  the  same  relative  positions,  though 
accurate  estimates  of  positions  were  not  attempted.  They  did  not  appear  to  me  to 
project  on  the  limb  of  the  moon,  as  described  by  observers  with  the  naked  eye,  and 
by  some  who  had  the  aid  of  telescopes,  and  is  so  conspicuous  in  the  photographs,  espe- 
cially where  the  exposure  was  prolonged.  This  lapping  on  the  edge  of  the  moon  was 
especially  noticed  in  the  large  prominence  on  the  southwest  or  lower  limb.*  But  my 
impression  the  day  after  the  eclipse  remained  distinct  that  the  moon's  limb,  under  this 
as  the  other  prominences,  appeared  smooth  and  unbroken,  although  no  note  was  made 
of  it  at  the  time. 

The  darkness  during  the  totality  was  not  as  great  as  I  anticipated,  as  I  was  able, 
with  but  little  difficulty,  to  write  in  my  note-book. 

Mr.  Rock  7iotes  that  "during  totality,  fire-flies  were  seen,  as  at  night ;  katydids  com- 
menced to  chirp ;  the  landscape  continued  visible  ;  a  bright  orange-purple  light  encir- 
cled the  horizon,  fading  into  the  dull,  ashen  hue  of  the  zenith." 

THE    SUN'S   RE-APPEARANCE LAST   CONTACT. 

Straggling  points  of  bright  light,  rapidly  spreading  and  uniting,  soon  formed 
a  slender,  brilliant  line,  regular  and  unbroken,  as  just  before  the  sun's  disappearance. 
It  seemed  the  work  of  an  instant,  and  corona  and  prominences  vanished  from  view. 
The  whole  was  a  shifting  scene  of  superb  magnificence,  occupying  what  seemed  to 
be  a  very  brief  moment  of  time. 

The  time  of  the  re-appearance  of  the  sun  was  noted  at  I3h  54™  32"  by  chronom- 
eter, or  5h  om  30".  2  local  mean  time.  This  may  have  been  too  soon,  although  I 
thought  myself  sufficiently  guarded  against  mistaking  the  increasing  glow  for  the 
actual  re-appearance  of  sunlight. 

The  last  contact  was  noted  at  i4b  50™  41"  by  chronometer,  or  5h  56™  30'. 2  local 
mean  time. 

*  It  was  spokeo  of  by  by-etanders  as  a  bole  cut  in  the  edge  of  the  moon. 
4  E   S 


26  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

COLLECTED    RESULTS. 

The  following  are  the  collected  mean  times  at  the  eclipse  stations  in  Burlington 
of  the  several  phases  of  the  eclipse.  They  are  ls.51  less  than  the  Burlington  mean 
time  for  Miss  Mitchell's  observations,  OM1  less  for  the  rest 

First  contact. 

Predicted  from  American  Ephemeris 3''  56™     2".  5 

Observed  by  Professor  Coffin - 1 28.5 

(  suspected n8.5 

Observed  by  Dr.  Gould,  on  screen,  <  . 

J  '  (  certain 14 .  .5 

Observed  by  Professor  Young,  with  spectroscope.  ......  7".  2 

Observed  by  Mr.  Stockwell,  on  screen 1 7S.6 

Observed  by  Professor  Eaton,  on  screen 238-5 

Observed  by  Miss  Mitchell 1 39.8 

Beginning  of  totality. 

Predicted  from  American  Ephemeris 4h  57'"  27s.  i 

Observed  by  Professor  Coffin 44s-6 

Observed  by  Dr.  Gould,  (supposed  3s  too  late) 438-7 

Observed  by  Mr.  Stockwell,  on  screen 4O8-7 

Observed  by  Professor  Eaton,  on  screen 3 9s- 7 

Observed  by  Miss  Mitchell 378-7 

End  of  totality. 

Predicted  from  American  Ephemeris 5h     om   i88.7 

Observed  by  Professor  Coffin 30". 2 

Observed  by  Dr.  Gould 34". 2 

Observed  by  Mr.  Stockwell,  on  screen 28s.  2 

Observed  by  Professor  Eaton,  on  screen 3  is.2 

Observed  by  Miss  Mitchell 258.6 

Last  contact. 

Predicted  from  American  Ephemeris 5h  56™  25".3  • 

Observed  by  Professor  Coffin 3O8.2 

Observed  by  Dr.  Gould,  on  screen 348-2 

Observed  by  Mr.  Stockwell,  on  screen 3 18.2 

Observed  by  Professor  Eaton,  on  screen 3  is.2 

Observed  by  Miss  Mitchell 29B.8 

METEORS. 

A  paragraph  in  the  newspapers,  a  few  days  afterward,  reminded  me  that  just 
before  totality  several  bright  flakes  swept  over  the  field  from  east  to  west,  or  more 
nearly  east-northeast  to  west-southwest,  appearing  like  thistle-blows  floating  in  the 
sunlight.  Similar  appearances  were  noticed  elsewhere,  but  their  meteoric  character  is 
very  questionable. 

Meteors,  however,  appear  to  have  been  noticed  during  the  eclipse  at  several 
places.  Mr.  Charles  G.  Boerner,  of  Vevay,  Ind.,  reports  that  during  the  total  phase 
several  meteors  were  seen  with  the  naked  eye,  by  some  of  their  most  reliable  citizens, 
about  45°  above  the  horizon,  their  path  being  in  a  westerly  direction.  One  counted 
three,  another  five,  quite  brilliant. 

J.  H.  C.  COFFIN. 


REPORT 


OF 


DR.  BENJAMIN  APTHORP  GOULD 


,  IOWA.. 


27 


REPORT  OF  DR.  B.  A.  GOULD. 


BURLINGTON,  IOWA. 

CAMBRIDGE,  August  14,  1869. 

DEAR  SIR  :  Having  availed  myself  of  your  kind  invitation  to  join  your  party  for 
observation  of  the  total  eclipse,  at  Burlington,  Iowa,  on  August  7,  I  lose  no  time  in 
transmitting  the  results  which  I  obtained. 

The  objects  to  which  I  proposed  to  give  special  attention,  beside  noting  the  times 
of  the  contacts,  were,  in  the  first  place,  a  determination  of  the  form  and  dimensions 
of  the  corona ;  and,  secondly,  a  sweep  along  the  ecliptic  during  the  total  phase,  in 
order  to  learn  whether  any  planet  might  be  visible  within  the  orbit  of  Mercury. 

For  these  purposes,  it  seemed  desirable  to  unite  width  of  field  with  as  much  light 
as  possible,  and  I  brought  an  equatorially-mounted  comet-seeker,  having  a  clear  aper- 
ture of  5  and  a  focal  length  of  35  English  inches.  This  somewhat  peculiar  telescope 
was  constructed  for  me,  a  few  years  since,  by  Tolles,  ithen  of  Canastota,  N.  Y.,  and 
now  superintendent  of  the  Boston  Optical  Works.  With  its  small  focal  length,  it  com- 
bines great  sharpness  of  definition  ;  and  for  this  occasion,  Mr.  Tolles  provided  it  with 
an  eye-piece  of  very  low  power,  which  affords  a  field  somewhat  exceeding  i  °  45'  in 
diameter,  and  is  traversed  by  a  glass  slide  bearing  three  dark  circles,  of  the  diameters 
4 1 '.6,  5 1 '.2,  and  64'. o,  respectively.  These  were  intended  for  the  double  purpose  of 
affording  an  approximate  estimate  of  the  dimensions  of  the  corona,  and  also  of  occult- 
ing its  light,  to  allow  a  better  perception  of  any  minute  or  faint  objects  in  the  vicinity 
of  the  sun. 

A  contrivance  for  measuring  the  diameter  of  the  corona,  as  seen  by  the  naked 
eye,  was  attached  to  the  telescope-tube.  It  consisted  of  a  firm  steel  rod,  made  of  a 
form  adapted  to  resist  flexure,  and  traversed  by  a  metal  carriage,  bearing  a  blackened 
disk  of  0.25  inch  diameter.  This  rod  was  graduated  throughout  its  whole  length,  and 
nicely  adjusted  parallel  to  the  optical  axis  of  the  telescope,  and  at  the  end  nearest  the 
eye  it  carried  a  circular  screen,  perforated  with  a  sight-hole.  Preliminary  trials  upon 
the  sun  gave  the  diameter  with  a  probable  error  not  exceeding  the  quarter  of  a  minute. 

The  shade-glasses  available  for  observation  of  first  contact  with  this  instrument, 
using  a  sufficiently  high  power,  proved  inadequate,  even  when  the  aperture  was  much 
diminished ;  and  I  availed  myself  of  the  kindness  of  the  Rev.  James  F.  Clarke,  of 
Boston,  who  was  near  me  and  offered  the  use  of  his  4-inch  telescope.  But,  scarcely 
half  a  minute  before  the  computed  time  of  first  contact,  the  shade-glass  of  this  tele- 
scope suddenly  cracked,  and  I  hastened  to  another  instrument  near  by,  a  23-inch 
telescope  of  45  inches  focal  length,  by  Alvan  Clark,  which  had  been  brought  by 
Prof.  C.  A.  Young,  of  Dartmouth  College,  and  was  provided  with  a  screen  of  white 
card-board,  on  which  the  solar  image  was  projected  with  a  diameter  of  perhaps  6 

inches,  or  a  little  more.  < 

29 


30  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

At  i2h  50™  3s  chronometer-time,  3h  56™  i  is.5  local  mean  time,  I  suspected  a  con- 
tact, and  at  1 2b  5om  6*  all  doubt  was  removed  by  a  well-marked  indentation  at  this 
point,  This  observation,  however,  is  superseded  by  the  successful  execution  of  the 
beautiful  idea  of  Professor  Young,  who  observed  upon  the  spectroscope  the  gradual 
extinction  of  the  brightest  line  of  the  chromosphere,  thus  obtaining  a  sharp  deter- 
mination of  the  time  of  first  contact,  (corresponding  to  the  complete  disappearance  of 
this  bright  line,)  and  an  excellent  measure  of  the  thickness  of  the  luminous  chromo- 
sphere itself;  and  introduced  a  method  of  observing  first  contacts  which  can  scarcely 
fail  to  receive  general  adoption  hereafter. 

The  sky  was  almost  cloudless,  and  the  atmosphere  much  more  transparent  and 
clear  than  usual  had  been  clarified  by  the  heavy  thunder-storms  of  the  preceding 
day.  As  the  moon  passed  gradually  over  the  sun's  disk,  the  well-known  phenomena 
occurred,  so  often  described.  The  light  grew  cold  and  weird,  the  heavens  assumed  a 
grayish  and,  finally,  an  almost  leaden  hue,  and  the  outlines  of  shadows  became  pre- 
tematurally  sharp  and  distinct.  I  examined  the  cusps  carefully  with  two  different 
telescopes,  by  direct  vision  with  powers  of  from  5<7  to  80,  and  also  on  the  screen,  btit 
could  discover  no  blunting  or  marked  rounding  of  the  extremities  at  1 3h  43™,  1 3h  45™, 
or  i3h  50™.  The  sky  at  ih  50 £m  was  of  a  cold  gray  color,  shading  off  into  blue  at  the 
horizon.  A  glance  through  a  field-glass  at  the  landscape  along  the  broad  expanse  of 
the  Mississippi,  which  was  visible  between  wooded  shores  for  some  1 2  or  1 5  miles  to 
the  northward,  showed  the  coloring  of  all  objects  reduced  to  an  almost  uniform  tint, 
not  unlike  that  imparted  under  ordinary  circumstances  by  the  use  of  a  light-shade 
glass  of  "  London  smoke." 

At  i3h  51™  1 5s,  a  plate  of  purple  glass  of  not  much  deeper  tint  than  I  have  seen 
used  for  the  windows  of  photographic  establishments,  sufficed  to  render  vision 
agreeable  with  the  full  aperture  of  my  telescope.  Through  this,  the  corona  was 
distinctly  visible  on  the  preceding  side,  as  well  as  above  and  below.  It  had 
already  been  visible  for  some  time  through  the  field-glass,  and  General  Wild, 
who  was  using  a  binocular  glass  of  about  2  inches  aperture,  with  a  light  shade,  had 
seen  it  at  i3h  50™  19". 

For  the  moment  of  total  obscuration,  I  consider  my  observation  as  uncertain  by 
two  seconds.  Anticipating  a  sudden  and  strongly-marked  phenomenon,  which  would 
permit  no  doubt  as  to  the  instant  of  its  occurrence,  the  great  brilliancy  of  the  pho- 
tosphere, or  perhaps  of  the  corona  at  the  last  point  of  occupation,  led  me  to  suppose 
the  totality  still  incomplete,  when  the  simultaneous  ejaculutions  of  the  crowd  assem- 
bled around  our  place  of  observation,  and  which  till  that  instant  had  maintained  abso- 
lute silence,  convinced  me  that  it  had  already  taken  place.  I  have  recorded  the 
moment  of  totality  as  i3h  51™  45",  4h  57m  43". 7  local  mean  time;  but  this  estimate 
was  made  certainly  three  seconds  later.  Previous  to  this,  the  thread  of  solar  light  had 
appeared  broken  into  several  fragments — not  beads,  but  patches  many  heliocentric 
degrees  in  length.  These  had  disappeared,  and  only  at  the  point  of  last  occupation 
was  the  brilliancy  maintained,  which  I  erroneously  supposed  to  belong  to  the  body  of 
the  sun. 


REPORT  OF  DR.  GOULD.  31 

Analogous  remarks  will  apply  almost  equally  well  to  my  observation  of  the  end 
of  totality,  which  took  place  a  few  seconds  before  I  expected,  and  while  my  attention 
was  directed  to  a  part  of  the  limb  at  some  little  distance  from  the  point  of  appearance 
of  the  first  ray.  I  recorded  it  as  13''  54™  36",  5b  oul  34".2  local  mean  time,  which 
is  not  improbably  too  late,  although  in  this  case  the  involuntary  buzz  of  the  crowd  was 
subsequently  heard. 

Indeed,  I  now  entertain  serious  doubts  whether,  with  a  power  so  low  as  that  which 
I  was  using,  (amounting  to  riot  more  than  five  diameters,)  and  with  an  amount  of  light 
relatively  so  large,  the  beginning  or  end  of  totality  can  be  well  determined  without  an 
error  to  be  apprehended  not  less  than  two  seconds.  The  brilliant  light  of  the  luminous 
envelope  at  the  point  of  disappearance  and  re-appearance  of  the  sun's  limb,  when  con- 
centrated by  a  lens  collecting  more  than  3.000  times  the  light  normally  admitted  to 
the  pupil,  yet  witli  so  slight  an  enlargement  of  the  image,  exhibits  an  intensity  scarcely, 
if  any,  less  than  125  times  that  recognized  by  the  unassisted  eye;  but  had  a  power 
of  55  or  60  been  employed,  the  increase  of  intensity  afforded  by  the  object-glass 
would  have  been  counterbalanced  by  the  magnifying  power  of  the  eye-piece,  and  the 
intensity  of  the  light  at  these  points  would  not  have  differed  essentially  from  that  per- 
ceived by  an  observer  without  a  telescope.  The  beginning  and  end  of  totality  usually 
described  as  occurring  with  such  extreme  suddenness  as  to  admit  of  determination 
within  a  small  fraction  of  a  second,  would  seem  nevertheless  not  to  be  instantaneous 
phenomena,  absolutely  speaking,  but  in  some  degree  subjective,  although  giving  the 
impression  of  instantaneousness,  being,  in  fact,  dependent  upon  the  occultation  of  a  pho- 
tosphere, the  brilliancy  of  which  diminishes  with  the  distance  from  the  hidden  surface 
of  the  sun.  If  this  view  be  correct,  the  appearance  and  disappearance  of  the  totality 
riiust  depend  in  some  degree  upon  a  limit  of  perception  in  the  observer,  and  its  dura- 
tion being  lessened  by  an  increase  of  the  relation  of  light  to  magnifying  power  in  the 
telescope.  And  the  correctness  of  the  opinion  may  be  tested  in  a  future  eclipse  by 
applying  the  spectroscopic  method  of  Professor  Young  to  the  determination  of  the 
second  and  third  as  well  as  of  the  first  contact.  Then,  with  a  telescope  of  large  aper- 
ture the  bright  spectral  lines  of  the  photosphere  ought  to  be  distinctly  seen  for  a  short 
interval  after  the  solar  spectrum  has  vanished,  and  again  before  its  re-appearance;  and 
the  length  of  this  interval  would  afford  a  measure  of  the  limits,  between  which  the 
time  of  total  obscuration  would  be  dependent  upon  the  optical  implements  employed. 

My  friends,  Messrs.  A.  C.  Baldwin,  of  Boston,  and  John  N.  Stockwell,  of  Brecks- 
ville,  Ohio,  and  General  Edward  A.  Wild,  of  Austin,  Nevada,  were  near  me,  the  first 
being  prepared  to  read  the  indications  upon  the  graduated  rod,  and  the  second  being 
near  the  declination  circle  to  read  this  off  in  case  of  need,  while  the  last  named  mapped 
for  me  at  sundry  different  moments  the  form  of  the  corona,  and  the  position  of  the 
protuberances.  Each  of  them  also  noted  sundry  points  to  which  I  had  asked  their 
special  attention  in  advance,  as  also  did  my  friend,  Mr.  Samuel  S.  Greeley,  city  sur- 
veyor of  Chicago. 

The  brilliancy  of  the  corona,  its  extent,  and  the  great  irregularity  of  its  form, 
were  sources  of  surprise  to  me.  Throughout  the  period  of  totality  the  daylight  was 
amply  sufficient  for  making  and  reading  pencil-memoranda  without  conscious  effort; 


32  ECLIPSE  OF  THE  SUN,  AUGUST  7,  18(59. 

but  Mr.  Baldwin  was  obliged  to  use  a  lantern  for  reading  the  graduations  of  the  steel 
rod,  which  were  in  a  very  unfavorable  position. 

A  rapid  survey  with  the  opera-glass,  immediately  after  the  occurrence  of 
totality,  showed  nothing  essentially  different  from  what  was  visible  to  the  telescope  or 
the  naked  eye.  The  corona,  as  seen  through  the  telescope,  seemed  a  little  larger,  and 
less  jagged  and  irregular  in  outline.  Venus  and  Mercury  were  very  prominent  objects, 
the  latter  shining  with  a  light  as  ruddy  as  Mars  ;  and  Regulus  was  easily  seen,  midway 
between  Venus  and  the  Sun.  A  moment's  glance  toward  the  zenith  showed  Arcturus, 
then  nearly  on  the  meridian ;  and  my  companions  had  no  difficulty  in  recognizing 
Mars  and  Saturn,  as  well  as  sundry  fixed  stars. 

Just  to  the  left  of  the  lowest  point  of  the  moon,  a  large  protuberance  was  con- 
spicuous to  the  unaided  eye.  This  I  estimated  as  not  less  than  ten  heliocentric  degrees 
wide,  and  on  the  average  nearly  two  minutes  high ;  but  this  estimate  was  hastily  and 
roughly  made.  In  general,  I  had  no  time  and  made  no  effort  to  fix  the  position 
either  of  this  or  of  any  of  the  other  protuberances,  but  General  Wild  entered  them 
approximately  on  his  charts.  This  largest  one  was  to  the  naked  eye  brilliantly  white; 
through  the  opera-glass,  it  was  tinted  with  rose-color,  so  as  to  contrast  with  the  yet 
whiter  light  at  the  base  of  the  corona;  but  through  the  telescope  it  appeared  strongly 
tinged  with  red,  especially  along  the  summit,  and  some  forked  tongues  protruded 
nearly  from  the  middle  by  nearly  a  minute  in  addition,  so  that  the  total  height  appeared 
not  far  from  one-tenth  of  the  lunar  diameter.  An  unmistakable  peculiarity  of  this 
protuberance  was  that  it  appeared  strongly  projected  upon  the  dark  limb  of  the  moon. 
This  was  the  case  whether  seen  with  the  unaided  eye,  the  opera-glass,  or  the  telescope, 
and  is  supported  by  the  concurrent  testimony  of  all  the  observers.  Casual  spectators, 
unfamiliar  with  astronomy,  insisted  vehemently  that  a  piece  had  been  missing  from 
the  moon's  limb,  allowing  the  sunlight  to  pass  through.  One  quite  intelligent  man 
compared  the  moon  to  a  cheese  from  the  rim  of  which  a  small  notch  had  been  cut. 
Mr.  Stockwell  describes  it  as  presenting  the  form  generally  of  a  deep  gorge  or  chasm, 
through  which  the  light  issued,  but  sometimes  actually  resembling  an  orifice  in  the 
body  of  the  moon,  being  completely  projected  upon  the  disk.  This  observation  seems 
to  explain  the  well-known  and  often-ridiculed  assertion  that  the  sunlight  has  been 
jen  in  former  eclipses  through  an  aperture  in  the  moon. 

At  about  I3h  52™  1 5s,  I  set  the  sliding  disk  cup  on  the  rod,  to  occult  the  corona  from 
the  naked  eye.  The  very  irregular  form  of  the  corona  rendered  this  more  difficult 
and  time-consuming  than  I  had  anticipated.  My  endeavor  was  to  gauge  the  average 
size  of  the  corona,  irrespective  of  the  specially -projecting  rays,  and  without  regard  to 
the  position  of  the  moon,  as  concentric  with  it,  or  otherwise.  After  the  brightest  part 
had  been  screened  off,  fainter  portions  at  the  circumference  became  distinctly  visible, 
and  required  a  new  setting  of  the  disk,  after  which  yet  a  third  similarly  became 
needful.  The  best  setting  which  1  succeeded  in  making  gave  at  i3h  52™  i68an  average 
diameter  of  63'. 6,  biit  left  five  large  beams  projecting  beyond  the  rim  of  the  screen; 
thus  indicating  a  general  height  of  about  16'  above  the  surface  of  the  sun,  or  an 
altitude  equal  to  its  whole  semi-diameter  even  when  we  disregard  the  prominent  beams 
or  streamers  of  which  one  at  least  extended  to  nearly  or  quite  twice  this  distance. 


REPORT  OP  DR.  GOULD.  33 

This  height  of  16'  is  above  the  true  average  for  the  corona  in  general,  inasmuch  as 
there  were  depressions  which  were  likewise  disregarded;  and  it  may,  moreover,  have 
been  apparently  exaggerated  by  diffraction,  although  no  pains  were  spared  to  avoid 
this  source  of  error.  But  the  luminous  envelope  must  certainly  have  extended  to  as 
rmich  as  15'  beyond  the  sun's  limb,  through  three-fourths  of  the  circumference,  and 
in  several  parts  it  exceeded  this  limit  considerably.  Still  a  measurement  similarly 
made  for  so  much  of  the  corona  as  was  conspicuous  to  the  eye  without  screening  off 
the  most  brilliant  central  portion  would  hardly  have  exceeded  54',  corresponding  to  a 
height  of  about  1 i'. 

The  five  prominent  beams  which  projected  beyond  the  general  outline  were  care- 
fully mapped  for  three  special  moments  by  General  Wild;  and  his  sketches  have 
given  much  assistance  to  me  in  connection  with  my  own  far  more  hurried  ones,  in  the 
subsequent  endeavors  to  delineate  the  form,  and  in  recalling  the  outlines  to  my 
memory.  Messrs.  Baldwin  and  Greeley  also  noted  the  position  of  the  projecting  beams; 
and  I  was  thus'able  at  the  first  convenient  opportunity  to  construct  drawings  of  the 
form  and  dimensions  of  the  corona,  for  the  beginning,  middle,  and  end  of  the  totality. 
My  drawings  have  been  reproduced  in  a  more  artistic  form  by  an  accomplished  friend, 
who  has  faithfully  represented  the  general  effect  in  the  delineations  herewith  inclosed. 
(Plate  II,  Figs,  i,  2,  3.)  They  represent  the  positions  as  seen  by  direct  vision,  the  ver- 
tex being  at  the  top  of  the  drawing  and  the  north  point  of  the  limb  about  53°  to  the 
right,  or  preceding,  side.  It  will  be  remarked  that  the  directions  of  the  most  promi- 
nent beams  corresponded  approximately  to  the  vertex,  and  the  four  cardinal  points"; 
also,  that  the  aspect  of  the  whole  corona  varied  materially  from  minute  to  minute,  though 
hardly  in  such  a  way  as  to  indicate  that  the  irregularities  of  form  were  affected  by  the 
position  or  contour  of  the  moon.  Nor  do  they  seem  to  stand  in  any  manifest  relation 
to  the  sun's  equator,  the  position  of  which  is  show.n  upon  the  drawings. 

The  largest  beam  pointed  south,  having  at  this  time  a  base  of  about  50°  and  a 
vertex  perhaps  10°  or  12°  wide,  as  measured  from  the  center.  Its  extent  beyond  the 
screen  I  estimated  as  not  less  than  10'  or  12'  of  a  great  circle,  making  its  total  height 
not  far  from  43'  from  the  center,  or  27'  from  the  surface  of  the  sun.  Another,  nearly 
as  large,  and  of  the  same  general  form,  projected  similarly  toward  the  preceding  side 
nearly  in  a  parallel  of  declination.  Two  smaller  ones  were  a  little  above  the  north 
point,  and  nearly  at  the  vertex  respectively ;  and  a  fifth,  the  smallest  and  obtusest  of 
all,  pointed  a  little  southward  on  the  following  side,  and  nearly  toward  Regulus, 
extending  less  than  two  minutes  beyond  the  screen. 

My  telescope  was  in  such  a  position  (circle  preceding)  that  the  graduated  outer 
face  of  the  steel  rest  was  inclined  downward  by  more  than  45°,  and  was  hardly  more 
than  a  meter  from  the  ground.  The  graduation  is  in  strong  black  lines,  about  one 
millimeter  in  breadth ;  but,  as  has  been  already  stated,  these  lines  were  not  distinct 
enough  against  the  gray  steel  for  Mr.  Baldwin  to  see  them  without  a  lantern. 

I  next  introduced  the  glass  slide  into  the  telescope,  and,  disregarding  as  before 
the  long  streamers,  of  which  the  two  on  the  following  side  had  become  considerably 
nearer  to  each  other  during  the  interval,  the  middle  circle  51'  in  diameter  was  found 
5  E  s 


34  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

to  hide  more  than  half  the  general  outline  of  the  corona;  although  when  the  circle  of 
40'  was  tried,  the  luminosity  appeared  to  extend  beyond  it  in  all  directions  by  decid- 
edly more  than  a  quarter  part  its  diameter.  This  measurement  was  at  I3h  52m4o",  and 
we  may  therefore  consider  the  general  diameter  of  the  corona  at  that  time,  as  seen 
through  my  seeker  with  a  power  of  5,  to  have  been  a  little  more  than  56',  correspond- 
ing to  a  general  altitude  of  not  quite  10'.  How  far  the  difference  between  this 
measurement  and  the  former  may  be  owing  to  the  use  of  the  telescope,  or  how  far  it 
may  be  due  to  actual  change  of  apparent  dimension,  are  questions  upon  which  I  am 
unable  to  form  an  opinion,  since  no  time  was  available  for  repeating  the  measure  with 
the  naked  eye. 

The  largest  occulting  circle,  64'  in  diameter,  was  then  pushed  over  the  sun,  hiding 
all  the  streamers  except  the  extremity  of  the  southern  one,  which  would  thus  appear 
to  have  been  at  least  if  or  18'  in  height,  inasmuch  as  the  opposite  one  was  shorter, 
and  the  center  of  the  circle  probably  south  of  the  sun's  center. 

With  my  eye  thus  protected  from  the  light  of  the  corona,  I  devoted  some  25 
seconds  to  a  careful  scrutiny  of  the  immediate  vicinity  of  the  sun,  in  order  to  ascer- 
tain whether  any  other  luminous  body  might  be  visible  there.  My  field  gave  a  range 
of  fully  20'  on  all  sides  beyond  this  circle,  but  I  could  discover  nothing  upon  the 
nearly  uniform  background  of  bluish-gray,  which  was  illuminated  unmistakably  by 
au  undefined  radiance  from  behind  the  circle.  Removing  the  slide,  a  slight  motion  of 
the  undamped  telescope  sufficed  to  throw  n  Cancri  into  the  field.  This  I  succeeded 
in  detecting,  although  with  difficulty,  thus  fixing  an  outer  limit  for  the  magnitude  of 
any  planetary  body  within  my  sweep  at  a  greater  distance  from  the  sun.  The  mag- 
nitude of  this  star  is  given  as  5M.8  by  Argelander  in  his  Durclimusterung,  and  was  also 
fixed  as  5M.8  in  my  Uranometrical  Determinations  at  Albany  in  1858.  Had  I  not  in 
advance  made  myself  familiar  with  its  position,  and  with  the  motion  necessary  to  bring 
it  into  the  center  of  the  field,  I  do  not  think  I  should  have  detected  it;  but  it  seems 
highly  improbable  that  any  star  surpassing  it  in  brightness  by  one  magnitude  could 
have  failed  to  arrest  my  attention,  even  in  that  close  proximity  to  the  sun's  limb, 
which  was  not  50'  distant,  although  out  of  the  field. 

The  position  of  the  ecliptic  was  well  marked  by  Mercury  and  Venus.  Between 
Mercury  and  the  sun,  no  star  was  visible.  This  distance  was  about  five  degrees,  and 
was  swept  through  in  about  30  seconds,  particular  attention  being  given  to  the  region 
nearest  the  sun.  Had  any  planet  as  bright  as  the  5th  magnitude  been  within  40'  of 
the  ecliptic,  it  could  hardly  have  failed  to  be  visible;  indeed,  I  think  that  any  object 
of  the  6th  magnitude  would  have  been  seen  if  not  within  2°  of  the  sun.  The  same 
process  was  then  repeated  on  the  other  side  in  the  direction  of  Venus,  which  required 
somewhat  more  care  and  time,  lasting  from  about  i3h  53™  45"  till  i3h  54m  20".  The 
limit  of  the  sweep  was  given  by  £  Leonis,  (5H.6,)  which  I  found  without  difficulty  by 
means  of  a  stop  previously  attached  to  my  declination  circle.  Starting  from  a  posi- 
tion about  one  degree  south,  and  one  degree  following  this  star,  I  moved  cautiously 
toward  the  sun,  but  saw  no  star  whatever  on  the  way,  though  very  thoroughly  scruti- 
nizing a  belt  at  least  i  °  in  width.  This  sweep  occupied  a  longer  time  than  I  had 
supposed,  and  on  reaching  the  sun,  the  increased  brilliancy  near  the  point  where  the 


REPORT  OF  DR.  GOULD.  35 

light  was  to  re-appear  warned  me  that  the  end  of  totality  was  close  at  hand.     It  did, 
indeed,  follow  within  five  seconds. 

Meanwhile,  a  range  of  protuberances  had  appeared  on  the  north-preceding  quad- 
rant. These  were  four  or  five  in  number,  and  their  variation  in  magnitude  was  evident 
from  the  order  of  their  appearance,  which  was  not  that  of  their  distance  from  the  point 
of  third  contact.  Their  positions,  and  the  order  of  their  appearance,  were  rioted  by 
General  Wild,  from  whose  memorandum  sketch  I  have  roughly  entered  them  upon 
the  drawing.*  Two  other  protuberances  visible  from  the  beginning  in  the  south  fol- 
lowing quadrant  were  occulted  toward  the  close  of  the  totality. 

I  had  asked  of  the  friends  I  have  named  attention  tp  the  tints  of  the  moon  and 
the  corona,  to  the  relative  distribution  of  light  in  the  corona,  and  to  some  other  points, 
all  of  which  I  myself  bore  in  mind.  Concerning  these,  the  testimony  of  all  is  accordant. 

The  form  of  the  corona  does  not  appear  to  have  been  essentially  modified  by  any 
subjective  influences.  Seen  with  either  eye  alone,  it  presented  the  same  aspect,  nor 
did  the  striations  or  projecting  beams  turn  in  the  least  when  the  observer  changed  the 
posture  of  his  head. 

Its  color  was  of  a  clear  brilliant  white  without  any  tinge.  Once  it  seemed  to  me 
to  have  a  very  slight  tinge  of  straw-color,  but  my  present  memory,  corroborated  by 
my  companions,  is  of  a  pure  white,  intensely  brilliant  at  the  base,  and  shading  rapidly 
by  imperceptible  gradations  to  its  outer  limit,  which  was  entirely  undefined  and  gray, 
fading  off  into  invisibility,  and  becoming  perceptible,  when  the  brighter  portions  were 
screened  from  the  eye,  to  a  much  greater  distance  than  it  could  otherwise  be  seen. 
There  were  no  concentric  strata  of  light  visible  to  me,  though  these  are  mentioned  by 
others.  The  projecting  beams  were  entirely  radial,  and  the  background  between 
them  seemed  filled  with  a  faint  diffuse  light.  The  basis  of  these  beams  or  streamers 
were  no  brighter  than  the  other  parts  of  the  corona  at  the  same  distance  from  the  sun. 
They  stood  in  no  apparent  relation  to  the  flame-like  protuberances,  or  to  the  sun's 
equator,  and  although  they  changed  their  positions  to  some  extent,  and  also  their 
dimensions  during  the  period  of  totality,  the  corona  did  not  appear  to  grow  constantly 
smaller  on  the  side  toward  which  the  moon  was  moving,  or  constantly  larger  on  the 
other  side.  That  no  such  change  as  this  took  place  I  am  not  prepared  to  say,  but  if 
there  was  any  it  was  only  to  a  small  extent.  The  projecting  beams  were  jagged  in 
their  outline  and  at  their  extremities,  and  when  two  approached  each  other,  as  in  the 
north-following  and  also  in  the  north-preceding  quadrant  at  the  middle  of  the  eclipse, 
these  seemed  like  streaming  remnants  of  some  pale,  tattered  banner.  A  radiating 
filamentous  aspect  was  strongly  marked. 

The  body  of  the  moon  was  not  of  the  intense  blackness  commonly  represented; 
this  impression  being  manifestly  due  solely  to  the  vivid  contrast  with  the  brilliant 
corona;  but  it  was  of  a  deep  slate-color,  a  very  dark  bluish-gray.  There  was  nothing 
of  olive  in  the  tint,  which  exhibited  no  apparent  admixture  of  yellow  or  green,  in 
however  small  degree. 

Of  the  protuberances  I  took  no  special  note  other  than  their  color,  and,  in  the 
case  of  the  large  one,  its  cellular  or  honeycombed  aspect  and  the  projection  of  its 

*  Their  positions  in  Plate  II  are  from  the  diagram  in  the  Report  of  Professor  Mayer,  Plate  X,  Figure  1. 


36  ECLIPSE  OF  THE  SUN,  AUGUST  7,  18G9. 

base  upon  the  moon's  disk.  This  last  very  striking  phenomenon  seems  due  to  an 
actual  reflection  of  the  intense  light  froift  the  surface  of  the  moon.  The  positions  of 
the  protuberances  upon  the  accompanying  drawings  are  taken  from  measurements  by 
others. 

Upon  the  reappearance  of  sunlight,  the  corona  faded  away  as  gradually  as  it  had 
appeared,  remaining  visible  on  the  opposite  side  of  the  moon  for  nearly  a  minute. 
Up  to  i4h  5m  the  cusps  showed  no  sign  of  blunting  or  rounding  at  their  extremities. 

The  last  contact,  like  the  first,  I  observed  upon  a  screen;  and  the  recorded  time, 
14''  50m  45s,  or  5h  56"'  348.2  local  mean  time,  is,  I  think,  a  good  determination. 
I  am,  my  dear  sir,  with  much  respect,  very  truly  yours, 

R  A.  GOULD. 
Prof.  JOHN  H.  C.  COFFIN, 

Superintendent  American  Ephemeris  and  Nautical  Almanac. 


SUPPLEMENTARY  REPORT  BY  DR.   B.  A.  GOULD. 

CAMBRIDGE,  October  25, 

DEAR  SIR:  A  careful  study  of  the  photographic  records  of  the  total  phase  of  the 
eclipse  has  led  me  to  some  inferences  which,  although  not  properly  belonging  within 
the  province  of  a  report  upon  the  results  of  personal  observation  at  the  time,  may  yet 
fairly  be  regarded  as  deductions  from  your  expedition.  J  therefore  avail  myself  of 
your  invitation  to  communicate  them,  as  an  appendix  to  my  report. 

Almost  the  first  impression  given  me  by  an  inspection  of  the  photographs,  made 
during  the  total  obscuration  at  Burlington  and  Ottumwa,  had  reference  to  the  very 
limited  extent  of  the  photographic  record  of  the  corona,  and  to  the  remarkable  defi- 
ciency even  of  this  record  at  two  nearly  opposite  points  of  the  limb,  where  no  such 
phenomenon  had  been  recognizable  by  the  eye.  A  comparison  with  my  sketches,  made 
near  the  beginning,  the  middle,  and  the  end  of  the  totality,  not  only  confirms  this 
impression,  but  shows  that  coronal  beams  had  been  especially  conspicuous  at  these 
parts  of  the  limb,  which  coincide  approximately  with  the  extremities  of  the  solar  axis. 

Soon  afterward,  I  had  an  opportunity  of  examining  the  photograph  taken  by  Mr. 
Whipple,  during  the  total  obscuration  at  Shelbyville,  Ky.  In  this,  which  was 
obtained  by  an  exposure  in  the  principal  focus  of  the  telescope  for  40  seconds,  one 
of  the  coronal  beams  (from  35°  to  45°  west  of  north,  as  nearly  as  I  can  estimate)  is 
depicted  to  the  height  of  at  least  7',  and  the  radiance  visible  about  the  polar  regions 
of  the  sun  is  here  also  decidedly  less  than  at  other  parts  of  the  limb.  None  of  the 
finer  details  of  the  protuberances  are  exhibited  in  this  photograph,  although  the  pro- 
tuberances themselves  are  recognizable  to  some  extent  from  their  superior  brilliancy 
to  that  of  the  surrounding  radiance. 

These  facts,  taken  in  connection  with  sundry  others,  and  especially  with  the  addi- 
tional one  that  the  coronal  beams  visible  to  the  eye  exhibited  no  relation  whatsoever 
to  the  protuberances,  whereas  the  aureole  shown  upon  the  photographs,  and  especially 


KEPOET  OF  DR.  GOULD.  37 

upon  those  of  short  exposure,  is  most  conspicuous  in  their  immediate  vicinity,  have 
suggested  what  I  cannot  but  believe  to  be  the  true  explanation  of  the  phenomena. 

Last  year's  eclipse  led,  as  is  well  known,  to  the  discovery  that  the  protuberances 
are  but  local  aggregations  of  a  brightly-glowing,  gaseous  medium,  which  surrounds 
the  solar  photosphere,  and  is  perceptible  by  the  spectroscope  at  any  part  of  the  sun's 
limb,  although,  like  the  protuberances  themselves,  it  is  less  abundant  near  the  poles. 
This  bright  envelope  has  received  from  Lockyerthe  name  "chromosphere";  its  outline 
has  been  found  to  be  quite  irregular,  jagged,  and  variable;  in  the  neighborhood  of  a 
protuberance  it  is  very  uneven  and  billowy,  while  at  other  parts  of  the  limb  it  is,  in 
general,  tolerably  uniform  in  height.  The  observations  of  both  Janesen  and  Lockyer, 
corroborated  by  other  investigators,  have  shown  that  the  light  of  this  chromosphere  is 
principally  due  to  incandescent  hydrogen  gas,  with  which  are  intermingled  the  vapors 
of  sundry  other  metals. 

The  large  quantity  of  photolytic  rays,  in  the  light  of  glowing  hydrogen,  would 
naturally  produce  a  prompt  and  distinct  record  upon  the  photographs,  and  the  facts 
observed  have  led  me  to  the  conviction  that  those  taken  at  Burlington  and  Ottumwa 
exhibit  merely  a  representation  of  this  chromosphere,  wider  and  more  irregular  in  its 
chemical  record  than  in  its  optical  image,  under  the  ordinary  circumstances  of  spec- 
troscopic  observation.  The  Shelbyville  photograph,  which,  as  I  have  said,  exhibits  a 
diminution  of  radiance  at  the  poles,  and  a  general  outline  altogether  unlike  that  of  the 
visible  corona,  manifests,  on  the  other  hand,  a  width  of  the  photographic  corona  singu- 
larly contrasting  with  the  slight  aureole  upon  the  much  larger  pictures  of  the  Nautical 
Almanac  parties,  who  gave  a  short  exposure  in  the  field  of  the  magnified  image.  If 
we  suppose  the  impression  there,  in  which  the  radiance  around  the  eclipsed  sun  is,  on 
the  average,  not  less  than  3'  or  3 £'  broad,  to  represent  anything  else  than  the  brightest 
portions  of  the  visible  corona,  we  encounter  serious  difficulties,  and  apparent  improb- 
abilities, it  is  true.  Yet  the  essential  diversity  of  its  form  from  that  of  the  visible 
corona  is  a  very  important  consideration,  and  the  fact  that  the  source  of  the  radiance 
exhibited  upon  the  photographs  is  materially  connected  with  the  body  of  the  sun  is 
established  by  its  manifest  relation  to  the  solar  axis,  while  the  rapid  variations  of  form 
in  the  visible  corona  would  suggest  the  reverse. 

Therefore  it  is  that,  notwithstanding  the  apparent  improbability  of  the  idea,  I 
incline  to  the  opinion  that  the  glory  seen  around  the  sun's  image,  even  upon  these  pho- 
tographs of  longest  and  intensest  exposure,  is  something  distinct  from  what  was  seen 
by  the  spectators  of  the  eclipse,  and  that  the  corona  proper,  or  that  whose  outlines  are 
depicted  in  the  drawings,  is  an  independent  phenomenon,  the  light  from  which, 
although  poor  in  photolytic  rays,  conceals  from  sight  that  chromospheric  radiance  to 
which  the  photographs  bear  witness.  If  this  be  so,  it  would  seem  natural  to  infer  that 
the  visible  corona — at  least  so  much  of  it  as  attracts  the  observer's  attention — may  not 
be  physically  connected  with  the  body  of  the  sun,  but  may  even  have  its  origin  within 
our  own  atmosphere;  an  inference  which  the  observed  fluctuations  in  its  form  would 
tend  to  corroborate. 

These  suggestions  are  offered  with  some  diffidence,  but  they  appear  to  me 
quite  in  conformity  with  established  or  highly  probable  physical  facts.  They  accord 
extremely  well  with  the  observations  of  Lockyer  and  Miller,  and  with  the  solar  theory 


38  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

of  Faye.  They  lead,  moreover,  to  the  supposition  that  the  chromosphere  is  simply 
the  atmosphere  of  the  sun,  where  it  is  rendered  luminous  by  the  formation  and  pre- 
cipitation of  the  photospheric  material,  whose  vehement  ejection  from  the  sun's  inte- 
rior forms  the  protuberances,  and  which  is  dissipated  according  to  the  laws  of  gaseous 
diffusion,  while  its  constituent  elements  are  condensed  in  the  order  of  their  tempera- 
tures of  vaporization.  The  abundance  of  violet  and  ultra-violet  rays  in  the  spectrum  of 
hydrogen,  and  the  levity  and  low  temperature  of  vaporization  of  this  element,  seem  to 
afford  a  full  explanation  of  the  photographic  phenomena,  when  considered  in  connec- 
tion with  the  higher  radiant  capacity  of  the  condensed,  though  diffuse,  chromospheric 
matter,  which  has  recorded  itself  on  the  plates  of  short  exposure,  although  it  was  not 
perceptible  by  the  observer. 

This  last-mentioned  fact  was  manifested  by  De  La  Rue's  results  in  1860,  and  is 
still  more  fully  illustrated  by  our  present  experience;  for  a  considerable  number  of 
the  fleecy  aggregations  and  nebulosities,  shown  upon  the  photographs  of  short  expos- 
ure almost  as  distinctly  and  conspicuously  as  the  protuberances  themselves,  were 
unseen  by  the  observers,  no  matter  what  the  telescopic  powers  employed. 

These  views  apparently  imply  also  an  essential  identity  in  the  material  of  the 
chromosphere,  the  faculse,  and  the  photosphere,  and  they  explain  the  small  amount  of 
atmospheric  refraction  at  the  sun.  It  is  probably  needless  to  add,  that  while  the  chro- 
mosphere should  theoretically  manifest  the  same  lines  as  ordinary  sunlight,  although 
reversed,  still,  its  inferior  brightness,  and  the  different  heights  of  condensation  for  dif- 
ferent elements,  would  render  it  impossible  that  they  should  be  exhibited.  At  the 
same  time  the  intense  heat  and  the  comparative  faintness  of  the  sources  of  chromos- 
pheric light  would  essentially  modify  the  relative  intensity  of  the  lines.  The  various 
phenomena  of  the  spots,  the  darker  centers  observed  in  their  nuclei,  and  similar 
unquestioned  facts,  seem  to  me  strongly  corroborative  of  this  explanation. 

Hoping  to  be  excused,  if  I  have  transcended,  the  proper  limits  of  a  report,  by 
trespassing  too  far  upon  the  domain  of  theory, 
I  am,  very  sincerely,  yours, 

B.  A.  GOULD. 

Prof.  J.  H.  C.  COFFIN, 

Superintendent  American  Ephemeris  and  Nautical  Almanac. 


REPORT 


OF 


PROFESSOR  CHARLES  A.  YOUNG. 


39 


REPORT   OF   PROF.   C.   A.   YOUNG. 


BURLINGTON,  IOWA. 

HANOVER,  N.  H.,  November  8,  1869. 

DEAR  SIR  :  I  have  the  honor  to  submit  the  following  report  of  my  observations 
upon  the  eclipse  of  August  7,  as  a  member  of  the  party  under  your  direction  : 


INSTRUMENTS. 


The  spectroscopic  combination  employed  was  made  up  of  various  instruments 
belonging  to  the  apparatus  of  Dartmouth  College,  arranged  for  the  occasion  in  a  man- 
ner somewhat  different  from  anything  heretofore  used,  but  which  proved  efficient. 

The  spectroscope  proper  had  five  prisms  of  dense  flint-glass,  (French,)  with 
refracting  angles  of  45°,  and  faces  i\  by  3  inches  Its  telescope  and  collimator  (by 
Alvan  Clark)  had  each  an  aperture  of  2\  inches,  with  a  focal  length  of  about  17. 
The  telescope  was  provided  with  a  wire  micrometer,  and  magnified  fourteen  times. 
The  prism-box  was  so  connected  with  the  arm  which  carried  the  telescope  that  any 
motion  of  the  latter  by  the  tangent-screw,  which  brought  the  different  portions  of  the 
spectrum  into  the  field  of  view,  would  give  it  an  angular  motion  just  half  as  great, 
and  thus  keep  the  prisms  in  the  position  of  least  deviation  and  best  definition.  The 
instrument  gave  a  deviation  of  about  165°  and  a  dispersion  of  18°  betw'een  A  and  H, 
and  showed  all  the  lines  on  Kirchhoff's  and  Angstrom's  maps.  The  position  of  a  line 
could  be  determined  by  it  by  one  observation,  under  favorable  circumstances,  within 
one  division  of  Kirchhoff's  scale,  which  I  shall  employ  throughout  this  report  in  describ- 
ing the  lines  observed  in  the  spectrum.  The  slit  of  the  spectroscope  was  J  of  an  inch 
long,  and  of  adjustable  width.  During  the  eclipse,  it  was  kept  open  about  soo  of  an 
inch,  as  nearly  as  could  be  estimated. 

A  small  camera-lucida  prism  was  arranged  in  such  a  manner  that  it  could  be 
turned  up  in  front  of  the  slit,  covering  half  its  length,  and  thus  permitting  direct  com- 
parison between  any  spectrum  under  observation  and  the  air-spectrum  formed  between 
platinum  electrodes  by  the  spark  from  a  small  induction-coil  and  Leyden  jar.  It  was 
not,  however,  found  necessary  to  use  this  arrangement,  as  the  six  known  lines  of  the 
chromosphere  spectrum  furnished  the  needed  points  of  reference,  and  the  faint,  con- 
tinuous spectrum  of  the  corona  enabled  the  micrometer-wires  to  be  easily  seen  with- 
out the  necessity  of  any  further  illumination. 

The  telescope,  which  formed  the  image  of  the  sun  upon  the  slit,  was  a  so-called 
comet-seeker,  (by  Merz  &  Sons,)  of  4  inches  aperture  and  30^  focal  length.     An  eye- 
piece was  employed  which  made  the  image  upon  the  slit  about  2\  inches  in  diameter." 
I  think  the  eye-piece  important,  because  it  gives  an  easy  means  of  securing  an  exact 
6  E  s 


42  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

focus  of  the  sun's  limb  upon  the  slit  for  any  part  of  the  spectrum  under  observation  ; 
and  in  even  the  most  perfect  achromatics  this  focus  varies  so  greatly  for  the  different 
colors  that  it  requires  constant  attention. 

Upon  the  collimator  was  fastened  a  brass  disk,  to  which  was  glued  a  circle  of 
white  paper  about  2  inches  in  diameter,  with  an  orifice  at  its  center,  graduated  by  radi- 
ating lines  into  angles  of  ro°,  and  so  placed  that  its  center  coincided  with  the  center 
of  the  slit.  The  image  formed  upon  this  paper  disk  furnished  the  means  of  directing 
the  instrument  upon  any  portion  of  the  sun,  and  answered  every  purpose  of  a  finder. 
During  the  totality,  the  whole  circumference  of  the  moon  was  visible  upon  this  screen, 
with  the  red  prominences,  and  something  even  of  the  corona  itself.  The  radiating  lines 
also  enabled  me  to  fix  with  sufficient  accuracy  the  position  of  any  object  under  obser- 
vation on  the  sun's  limb,  or  to  bring  any  desired  point  to  the  slit,  as,  for  instance,  to 
obtain  the  spectroscopic  observation  of  a  contact. 

Of  course  this  arrangement  would  not  answer  for  the  observation  of  any  but 
bright  objects,  like  the  sun  and  rnoon,  whose  images  are  easily  visible  upon  a  screen. 

The  comet-seeker  and  spectroscope  were  attached  to  a  wooden  frame-work,  and 
the  whole  was  mounted  equatorially,  with  tangent-screws  for  slow  motion,  both  in  right 

ascension  and  declination. 

The    instrument   is  represented    in 
the  accompanying  figure. 

Besides  the  spectroscope,  I  also  took 
with  me  a  small  telescope  -of  2|  inches 
aperture  and  45  inches  focal  length, 
mounted  upon  a  pillar  and  claw-stand. 
This  was  fitted  with  screens  by  my  as- 
sistant, Mr.  Emerson,  in  such  a  manner 
as  to  cast  an  image  of  the  sun  about  6 
indies  in  diameter  upon  a  piece  of  Bristol 
board  carefully  shaded  from  all  sunlight 
except  what  came  through  the  instrument.  This  image  was  observed  upon  by  Dr. 
B.  A.  Gould,  of  Cambridge  ;  Professor  Eaton,  of  the  Packer  Institute,  and  others, 
who,  I  presume,  will  report  to  you  directly. 

I  had,  also,  a  spy-glass  of  2\  inches  aperture,  which  was  loaned  to  Rev.  W.  Salter. 
In  addition,  I  took  with  me  a  small   induction-coil,  capable  of  giving  a  spark  f 
of  an  inch  long ;  a  small  Leyden  jar,  and  three  cups  of  Bunsen's  battery,  two-quart 
jars ;  also,  a  pair  of  Nicol's  prisms,  and  an  excellent  plate  of  tourmaline. 

PRELIMINARY  OPERATIONS. 

I  arrived  in  Burlington  Tuesday  evening,  and  the  next  morning  (August  4)  the 
instrument  was  mounted  in  the  southwest  corner  of  the  building  provided  for  the  pho- 
tographic operations.  The  same  afternoon  a  few  micrometrical  measurements  were 
taken  on  the  principal  lines  of  the  spectrum  to  ascertain  whether  the  value  of  a  revolu- 
tion of  the  micrometer-screw  had  changed  by  any  displacement  of  the  prisms  during 
transportation.  The  results  appeared  satisfactory.  I  intended  to  make  a  thorough 


REPORT  OF  PROFESSOR  YOUNG.  43 

examination  of  the  whole  length  of  the  spectrum  before  the  eclipse,  such  as  I  had 
made  at  Hanover  previous  to  packing  up  ;  but  the  instrument  was  so  situated  in  the 
building  that  the  morning  sun  could  not  be  used,  and  the  afternoons  of  Thursday  and 
Friday  were  botli  most  discouragingly  overcast  and  rainy.  I  think,  however,  from 
the  measurements  made  on  Wednesday,  we  may  safely  assume  the  scale  of  the  instru- 
ment to  have  undergone  no  material  alteration. 

The  unfavorable  weather  prevented  any  further  operations  until  Saturday.  The 
forenoon  of  this  day  was  mainly  occupied  by  myself  and  assistant  in  setting  up  the 
batteries,  making  the  telegraphic  connections,  and  giving  what  other  aid  we  could  to 
the  members  of  our  party  in  the  arrangement  and  adjustment  of  their  instruments. 

SOLAR    PROMINENCES. 

In  the  afternoon,  before  the  commencement  of  the  eclipse,  I  examined  the  whole 
circumference  of  the  sun,  and  noted  protuberances  in  the  following  positions :  (The 
position-angles  are  reckoned  from,  the  north  toward  the  east.) 

1.  +  70°  to  4-  90°;  a  diffuse  mass  with  many  detached  clouds. 

2.  4-  146°;  very  bright,  but  not  large. 

3    —  130°;  an  enormous  and  very  bright  protuberance — the  principal  one. 
4.  --  7o°-75°;  a  long,  low,  but  pretty  bright  mass. 

Besides  these,  several  smaller  ones  were  seen  whose  positions  were  not  noted 
owing  to  the  near  approach  of  the  eclipse. 

FIRST    CONTACT. 

I  had  not  intended  to  make  any  observation  upon  the  time  of  contact,  considering 
the  spectroscope  an  unsuitable  instrument  for  the  purpose;  but  about  half  an  hour 
before  the  event  was  to  take  place  it  occurred  to  me  that,  on  the  contrary,  th'e  spectro- 
scope could  be  made  to  give  results  superior  in  value  to  any  that  could  possibly  be 
obtained  by  other  methods,  excepting,  perhaps,  the  data  deduced  by  calculation  from 
measurement  upon  photographs.  Accordingly,  I  connected  myself  with  the  chrono- 
graph. 

When  the  telescopes  and  collimator  of  the  instrument  are  properly  focused,  and 
the  limb  of  the  sun  is  made  to  bisect  the  slit  nearly  at  right  angles,  the  spectrum  in 
the  neighborhood  of  the  C  line  presents  the  appearance  I  have  indicated  in  Plate  III, 
Figure  2.  Half  of  the  spectrum  will  be  brilliant,  and  the  other  half,  formed  mainly 
by  the  illuminated  air  just  beyond  the  edge  of  the  sun,  comparatively  obscure.  Most 
of  the  dark  lines  on  the  bright  portion  of  the  spectrum  will  continue  directly  across 
the  dusky  portion.  Not  so  the  C  line,  however,  which  terminates  at  the  edge  of  the 
brilliant  part,  to  be  replaced  in  the  dusky  spectrum  by  a  scarlet  line  running  up  like 
a  needle  of  light  to  a  height  depending  upon  the  thickness  of  the  chromosphere  at  the 
point  observed.  (The  chromosphere  being  the  stratum  mainly  of  incandescent  hydrogen 
which  overlies  the  photosphere,  and  was  first  so  named  by  Mr.  Lockyer.) 

In  my  instrument,  the  apparent  breadth  of  the  spectrum,  referred  to  the  limit  of 
distinct  vision  at  a  distance  of  10  ;nches,  is  almost  exactly  i^  inches,  and,  with  the 
eye-piece  used  on  the  comet-seeker  during  the  eclipse,  corresponds  to  a  width  of  2'  54" 


44  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

on  the  sun's  disk,  determined  by  the  time  occupied  by  the  sun's  limb  in  traversing 
the  slit,  which  was,  by  repeated  observations,  i28.62  on  the  gth  of  June.  This  very 
conveniently  gives  a  scale  of  almost  precisely  TOO  of  an  inch  to  the  second  of  arc. 

The  apparent  length  of  this  brilliant  needle  of  the  chromosphere  spectrum  usually 
ranges  from  6  to  1 2  hundredths  of  an  inch,  but  when  a  prominence  is  on  the  slit  it 
may  be  of  any  length,  depending,  of  course,  upon  the  height  of  the  protuberance. 

Now,  if  we  bring  to  the  slit  of  the  spectroscope  that  portion  of  the  sun's  limb  where 
the  contact  is  to  occur,  it  is  obvious  that  before  the  edge  of  the  moon  reaches  the  sun 
itself,  it  must  first  occult  the  chromosphere;  and  this  will  be  evident  to  the  observer 
with  the  spectroscope  by  the  gradual  shortening  and  final  extinction  of  the  brilliant 
needle  in  the  C  line;  or,  indeed,  in  any  other  line  of  the  chromosphere  spectrum,  as 
for  instance  F,  or  the  line  near  1)  at  1017.5,  now  usually  known  as  D3;  the  C  line  is, 
however,  by  far  the  best  adapted  to  observat'on. 

At  the  beginning  of  the  eclipse,  I  had  thus  the  pleasure  of  witnessing  the  gradual 
approach  of  the  moon,  visible  for  more  than  40  seconds  before  it  reached  the  sun, 
because  there  happened  to  be  a  prominence  of  considerable  brightness,  though  small 
elevation,  exactly  at  the  point  of  contact,  ( — 71°,)  which  made  the  needle  of  light 
nearly  J  of  an  inch  in  apparent  length.  The  moon's  arrival  was  first  signaled  by  the 
square  truncation  of  the  point  of  the  needle,  which  before  was  somewhat  acute;  then 
it  grew  perceptibly  shorter  (not  fainter)  second  by  second,  until,  at  i2h  49™  588.6  by 
the  chronometer,  (3h  56™  7".  3  Burlington  mean  time,)  its  last  spark  was  covered,  and  I 
recorded  the  contact.  I  think  the  observation  was  as  easy  and  as  accurate  as  a  star- 
transit,  (the  star  being  about  20°  from  the  pole,)  and  that  the  recorded  time  cannot 
possibly  be  more  than  £  a  second  in  error. 

The  gentlemen  who  observed  in  the  usual  methods,  first  noted  the  contact  (as 
might  be,  of  course,  expected,  since  they  could  only  perceive  the  event  after  it  had 
actually  occurred)  from  5  to  20  seconds  later;  but  I  am  informed  by  Professor  Mayer, 
who  had  charge  of  the  photographic  party,  that  the  time  deduced  by  a  computation 
based  upon  a  preliminary  measurement  of  two  of  the  photographs  taken  within  the 
first  minute  after  the  contact  was  announced,  agrees  with  my  observation  within  A 
of  a  second. 

I  am  fully  persuaded  that  hereafter  Lie  spectroscope  ought  to  be  considered 
indispensable  to  the  accurate  observation  of  the  first  contact  of  any  opaque  body  with 
the  sun's  limb,  and  properly  used  will  make  such  observations  as  easy  and  accurate 
as  those  of  any  other  appulsive  phenomena. 

[NOTE. — Since  writing  this  report,  I  have  received  volume  68  of  the  Comptes  Rendus  of 
tlie  French  Academy  of  Sciences,  and  find  that  I  have  been  anticipated  in  respect  to  this 
application  of  the  spectroscope  by  M.  Faye. 

At  the  session  of  Monday,  January  1 1,  1869,  in  a  discussion  relating  to  the  observa- 
tion of  Uie  approaching  transit  of  Venus,  he  proposed  essentially  the  same  method  of  observ- 
ing the  contact  which  I  employed  in  this  eclipse.  I  regret  that  I  was  not  earlier  aware  of 
this  fact. — Hanover,  November  16,  1869.] 

In  the  observation  of  the  approaching  transit  of  Venus  it  will,  I  believe,  prove 
of  special  value.  Of  course  it  is  not  yet  possible  to  say  precisely  how  much  this 
method  may  be  affected  by  the  planet's  atmosphere  and  by  irradiation;  but  it  is  diffi- 


REPORT  OF  PROFESSOR  YOUNG.  45 

cult  to  see  why  it  should  suffer  more  from  any  of  these  circumstances  than  the""older 
modes  of  observing;  and  the  astronomer  armed  with  the  spectroscope  will  have  this 
incalculable  advantage  over  all  his  compeers,  that,  some  time  before  the  contact 
actually  takes  place,  he  will  be  apprised  of  the  planet's  advent,  will  witness  her  gradual 
approach,  and  thus  be  able  to  concentrate  his  attention  on  the  one  important  moment 
instead  of  being  kept  upon  the  strain  for  minutes.  By  opening  the  slit  a  little,  as  is 
customary  in  making  drawings  of  the  prominences,  he  can  even  see  the  curved  out- 
line of  the  planet's  disk,  black  upon  the  scarlet  ground  of  the  chromosphere,  and  can 
select  the  precise  point  of  impact.  If  his  instrument  has  sufficient  dispersive  power, 
(at  least  twice  as  great  as  that  of  the  one  I  employed  on  this  occasion,)  and  is  provided 
with  an  accurate  clock-work,  he  can  place  the  slit  tangential  to  the  limb,  and  opening 
it  somewhat  widely,  can  command  the  chromosphere  for  several  degrees  on  each  side 
of  the  computed  point  of  contact,  and  thus  avoid  the  anxious  cruising  that  would 
otherwise  be  necessary  on  account  of  the  uncertainty  of  this  important  datum. 

It  would  seem  also  that  the  internal  contacts  might  be  observed  with  the  spectro- 
scope at  least  as  accurately  as  in  any  other  method;  for  the  phenomenon  to  be 
observed,  instead  of  being  merely  the  breaking  of  a  small  black  ligament,  will  be  the 
sudden  formation  of  a  line  of  brilliant  light  running  the  whole  length  of  the  spectrum — 
unless,  indeed,  the  planet's  atmosphei'e  introduces  some  unforeseen  complications. 


LUNAR    ATMOSPHERE. 


As  the  eclipse  proceeded,  special  attention  was  paid  to  the  action  of  the  moon's 
limb  upon  the  spectrum,  in  hopes  of  obtaining  some  evidence  of  a  lu-nar  atmosphere, 
however  rare.  The  results  were  wholly  negative ;  there  was  not  the  slightest  trace 
of  absorption-bands,  nor  did  the  ordinary  atmospheric  lines,  so  abundant  in  the  neigh- 
borhood of  D,  acquire  any  new  strength.  There  was  not  the  slightest  bending  or 
distortion  of  any  of  the  lines  at  the  moon's  limb,  but  whether  the  slit  were  radial  or 
nearly  tangential,  they  came  up  squarely  and  sharply  to  the  edge,  so  that  the  line  of 
demarkation  between  the  bright  and  dusky  portions  of  the  spectrum  was  perfectly 
hard  and  definite.  Just  before  the  commencement  of  the  totality,  when  the  visible  cres- 
cent of  the  sun's  image  was  narrower  than  the  slit,  the  contrast  between  the  effect  of 
the  moon's  limb  and  that  of  the  sun  was  beautifully  marked.  The  former,  as  I  have 
said,  gives  a  perfectly  defined  boundary ;  but  the  latter,  whatever  care  may  be  taken 
with  the  focus,  is  always  somewhat  indefinite  and  hazy,  and  there  is  no  abrupt  termi- 
nation of  the  dark  lines.  Still,  I  have  never  seen  any  trace  of  the  continuous  spec- 
trum described  by  Secchi,  and  am  sure  that  if  there  is  a  layer  on  the  sun's  limb,  giv- 
ing such  a  spectrum,  its  thickness,  instead  of  being  4"  or  5",  must  be  much  less. 

I  at  first  supposed  that  the  above-described  negative  evidence  would  be  almost 
decisive  against  a  lunar  atmosphere,  but  further  reflection  has  convinced  me  that  the 
facts  mentioned  are  not  in  the  least  inconsistent  with  the  existence  of  an  atmosphere 
two  or  three  thousand  times  rarer  than  our  own,  and  yet  sufficient  to  produce  a  refrac- 
tion of  4"  or  5",  and  thus  to  explain  the  crepuscle  of  light  around  the  moon's  limb,  so 
beautifully  evident  upon  the  photographs  of  the  partial  phases  of  the  eclipse.  Possi- 
bly, however,  this  crepuscle  may  yet  find  an  explanation,  as  a  special  case  of  diffraction, 
upon  purely  optical  principles,  without  the  necessity  of  assuming  a  lunar  atmosphere. 


46  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

SPECTRUM    LINES    OBSERVED    DURING    TOTALITY. 

At  the  commencement  of  the  totality,  my  instrument  was  directed  upon  the 
prominence  at  146°,  upon  the  southeast  border  of  the  sun,  and  just  before  the  dark- 
ness began  I  ran  back  my  instrument  to  the  neighborhood  of  the  B  line,  in  order  to 
examine  whether  any  bright  lines  existed  of  a  refrangibility  lo  wer  than  C.  The  last 
ray  of  sunlight  disappeared  almost  instantaneously,  and  I  now  greatly  regret  that  I 
did  not  record  the  moment  upon  the  chronograph ;  for  it  seems  that  to  the  observers 
with  the  telescope,  some  of  them  at  least,  it  was  a  gradual  event  occupying  two  or 
three  seconds.  But  I  supposed  it  could  be  far  better  observed  with  the  other  instru- 
ments, and  accordingly  confined  my  attention  strictly  to  the  spectrum.  As  soon  as 
the  last  sunlight  vanished,  the  C  line,  before  bright  and  conspicuous,  blazed  out  with 
brilliancy  fairly  dazzling,  though  it  reached  only  partly  across  the  spectrum,  because 
the  protuberance  upon  which  the  slit  was  directed  was  of  small  extent.  No  line 
appeared  below  it. 

While  my  assistant,  Mr.  Emerson,  with  an  accuracy  of  hand  which  answered 
almost  every  purpose  of  a  clock-work,  kept  the  limb  of  the  sun  exactly  on  the  center 
of  the  slit  by  means  of  the  right-ascension  tangent-screw,  I  swept  rapidly  over  the 
spectrum.  Between  C  and  D,  nothing  was  found.  Just  above  D,  shone  out  the  well- 
known  but  hitherto  mysterious  golden  D3  at  1017.5.  It  was  very  bright,  but  did  not 
equal  C.  Then  came  two  very  faint  lines,  of  nearly  equal  brightness,  situated  about 
1250  and  1350  of  KirchhofFs  scale,  as  nearly  as  I  could  estimate  from  their  relation  to 
D3,  and  the  1474  line,  which  came  next.  Their  exact  position  is,  so  far  as  my  observa- 
tion was  concerned,  doubtful  to  the  extent  of  twenty  or  thirty  scale-divisions. 

Next  above  them,  a  little  below  E,  appeared  the  line  which  I  had  before  seen  with 
so  much  difficulty  at  1474.  I  first  discovered  it  on  the  gth  of  July  ;  but,  as  I  have 
since  learned,  it  was  before  observed  by  Mr.  Lockyer  on  the  6th  of  June.  It  was 
also,  undoubtedly,  seen  by  Rayet  at  the  eclipse  of  August,  1 868,  thou  gh  by  him  mis- 
taken for  E. 

It  was  sufficiently  bright  to  be  conspicuous,  though  far  inferior  to  D3,  and  imme- 
diately attracted  my  attention  by  the  fact  that  it  extended  entirely  across  the  spectrum, 
which  was  not  the  case  with  C  or  D3.  Concluding  at  once  that  this  line  belonged  to 
the  spectrum  of  the  corona,  and  not  to  that  of  the  protuberance,  I  tested  my  idea  by 
simply  touching  the  declination  tangent-screw,  and  so  throwing  the  slit  off  from  the 
prominence.  The  D3  line,  which  was  visible  in  the  edge  of  the  field  at  the  same  time, 
immediately  disappeared,  but  1474  was,  if  anything,  brighter  than  before.  The  same 
was  true,  if  my  recollection  serves  me,  of  the  two  fainter  lines  between  it  and  D3 ;  but 
of  this  I  am  not  positive. 

The  question  has  been  raised  whether  these  lines  may  not  pertain  neither  to  the 
spectrum  of  the  prominences  nor  to  that  of  'he  corona  proper,  but  to  the  spectrum  of 
the  diffuse  nebulosity  which  is  shown  upon  the  photographs  as  surrounding  the  pro- 
tuberances. I  dare  not  assert  positively  that  this  may  not  be  the  case,  for  I  do  not 
know  precisely  how  far  I  removed  the  slit  from  the  prominence,  though  I  think  as 
much  as  5'  or  6'.  But  my  present,  though  hardly  very  confident,  belief  is  that  this  nebu- 


REPORT  OF  PROFESSOR  YOUNG.  47 

lo.sity  is  the  corona,  and  in  no  way  to  be  distinguished  from  the  rest  of  the  diffuse 
light  around  the  sun.  The  longer  the  exposure  of  the  plate,  the  more  nearly,  I  think, 
the  outline  of  the  photographic  corona  agrees  with  that  seen  by  the  eye,  as,  for  instance, 
in  the  beautiful  photograph  of  Mr.  Whipple  produced  by  an  exposure  of  forty  sec- 
onds. I  am  aware  that  some  most  eminent  observers  think  differently,  and  maintain 
that  the  actinic  corona  presents  entirely  a  different  outline  from  the  visible,  and  is  less 
extensive ;  and  for  that  reason,  as  I  said,  I  do  not  feel  certain  as  to  the  correctness 
of  my  view  ;  but  I  am  rather  confirmed  in  it  by  the  observation  of  Professor  Picker- 
ing. He  used  a  spectroscope  with  a  single  prism  of  60°,  having  no  lens  or  telescope 
to  throw  an  image  of  the  sun  upon  the  slit,  and  thus  obtained  a  spectrum  produced  by 
all  the  light  that  came  from  a  region  7°  or  8°  in  diameter  around  the  sun.  In  this 
case,  of  course,  the  brightness  of  any  particular  portion  or  line  of  the  spectrum  depends 
upon  the  absolute  quantity  of  light  of  that  special  refrangibility -which  comes  to  the 
instrument  from  the  whole  space  included  by  the  cone,  whose  base  is  the  object  glass 
of  the  collimator,  and  whose  vertex  is  the  center  of  the  slit,  An  extensive  faint  lumi- 
nosity may  in  this  case  have  as  powerful  an  effect  as  a  light  far  more  intense,  but  con- 
centrated into  a  smaller  angular  area.  Now,  in  my  instrument,  there  was  absolutely 
no  comparison  between  the  dazzling  blaze  of  the  C,  F,  and  D3  lines  and  the  subdued 
light  of  1474  ;  but  in  the  spectrum  seen  by  Professor  Pickering,  the  "  line  near  E  " 
was  much  the  brightest  •  their  relations  were  reversed.  I  think  this  shows  conclusively 
that  the  light,  to  which  is  due  the  1474  line,  must  be  diffused  over  a  far  more  extensive 
angular  surface  than  that  which  produces  the  other  rays.  It  does  not,  however,  show 
that  there  may  not  be  in  the  corona  other  light  besides  this.  Probably  there  is. 

To  return  from  this  digression.  By  the  time  I  had  carefully  examined  1474  the 
moon  had  advanced  so  far  that  it  became  necessary  to  transfer  the  slit  to  the  other 
edge  of  the  solar  image.  While  my  assistant  was  doing  this  by  the  tangent-screws,  I 
suppose  that  inadvertently  I  continued  to  move  the  spectrum  across  the  field  of  view, 
thus  passing  the  region  of  the  b  line  while  there  was  no  protuberance  upon  the  slit.  I 
have  no  distinct  recollection  .in  regard  to  this,  but  it  is  the  only  way  in  which  I  can 
account  for  not  seeing  this  line,  which  was  easily  seen  by  others,  as  I  have  since  learned. 
The  next  line  I  saw  was  the  F  line,  exceedingly  brilliant,  very  nearly  equal  to  D3,  perhaps 
a  little  brighter.  It  was  broad  at  the  base  and  tapered  to  a  fine  line  at  an  elevation  of  30" 
or  40"  above  the  limb.  On  account  of  the  great  size  of  the  prominence  upon  which  the 
instrument  was  now  directed,  and  the  oblique  position  of  the  slit,  it  reached  nearly,  if 
not  quite,  across  the  spectrum;  but  it  disappeared  as  soon  as  the  slit  was  moved  away. 
Passing  on,  a  new  line  about  as  bright  as  1474  made  its  appearance  above  F;  but 
without  stopping  to  measure  its  exact  position  then,  I  pushed  along.  Next  came  the 
2796  line  (hydrogen  7)  just  below  G,  and  soon  the  h  line  (hydrogen  £)  appeared  in 
the  edge  of  the  field  clear  and  bright,  though  less  so  than  2796.  My  impression,  but 
I  cannot  give  it  with  any  confidence,  is  that  I  saw  three  other  faint  lines  in  addition 
to  the  nine  I  have  named,  one  not  far  above  F  and  two  between  Gf  and  h.  I  failed  to 
note  them,  however.  Finding  nothing  above  h,  I  at  once  turned  back  to  determine 
the  position  of  the.  new  line*  between  F  arid  Gr.  I  obtained  a  satisfactory  measure- 

*  This  is  undoubtedly  the  line  referred  to  l>y  Lieutenant  Hersoliel  in  a  letter  to  Mr.  Hnggins  from  India,  dated  last 
July,  and  quoted  in  a  recent  number  of  tlie  Chemical  News. 


48  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1809. 

merit  upon  it,  as  I  supposed,  which  fixed  its  position  i  ir  38dlv  of  my  micrometer  screw 
below  2796  ;  that  is,  at  2602  of  Kirchhoff's  scale,  with  a  probable  error  of  2  or  3  divis- 
ions. 

A  brilliant  protuberance  observed  by  me  on  October  7,  however,  gave  a  line, 
very  distinct,  though  short,  at  2581.5;  and  from  this  circumstance  I  am  led  to  suspect 
an  error  of  a  whole  revolution  in  my  measurement.  If  there  be  such  an  error,  the 
result  of  this  measurement,  using  i2r  38div  instead  of  nr  38div,  as  recorded,  would  be 
2584,  which  accords  perhaps  as  well  as  could  be  expected  from  a  single  measurement 
under  so  exciting  circumstances.  Just  as  I  was  finishing  this  reading,  and  before  I 
could  examine  any  of  the  fainter  lines,  the  sun  burst  out.  They  disappeared  almost 
instantaneously,  but  2  796  remained  visible  for  several  seconds,  so  that  I  could  be  sure 
I  had  made  no  mistake  in  its  identification. 

Plate  III,  figure  1,  represents  the  spectrum  as  seen  by  me.  I  cannot  describe  the 
sensation  of  surprise  and  mortification,  of  personal  imbecility  and  wasted  opportunity, 
that  overwhelmed  me  when  the  sunlight  flashed  out.  I  think  it  was  shared  by  other 
observers  to  a  greater  or  less  degree. 

POLARIZATION. 

While  I  was  upon  the  1474  line,  I  examined  carefully  the  faint,  continuous 
spectrum  which  formed  the  background  for  the  bright  lines.  It  was  strong  enough 
to  have  its  edges  well  defined,  but  showed  not  the  slightest  trace  of  any  dark  line, 
though  my  instrument  shows  the  stronger  lines  plainly  in  spectra,  which  I  should 
judge  to  be  no  brighter,  formed  by  clouds  or  diffuse  daylight.  Testing  it  with  a  tour- 
maline held  in  the  hand  between  the  eye  and  the  eye-piece  of  the  spectroscope,  I  found 
that  when  the  axis  of  the  crystal  was  parallel  to  the  slit,  which  at  this  point  was  nearly 
perpendicular  to  the  sun's  limb,  the  light  seemed  to  be  unaffected;  but  on  placing  the 
axis  perpendicular  to  the  slit,  the  faint  continuous  spectrum  nearly  vanished  while  the 
bright  lines  remained  unchanged.  It  is  perhaps  not  impossible  that  the  polarization 
thus  manifested  may,  as  suggested  by  Professor  Pickering,  have  originated  in  the  suc- 
cessive refractions  through  the  ten  surfaces  of  the  prisms.  If  not,  the  absence  of  the 
dark  lines  in  the  faint  spectrum  is  certainly  a  very  puzzling  fact;  and  yet  the  ordinary 
solar  spectrum,  tested  in  the  same  way,  shows  no  sensible  polarization. 

•GENERAL   IMPRESSIONS. 

During  the  totality,  the  darkness  became  such  that  I  could  not  read  the  micrometer- 
head  without  artificial  light;  and  while  Mr.  Emerson,  at  my  request,  was  handing  me 
a  lantern  which  hung  in  readiness,  I  turned  my  head,  and  for  perhaps  loor  15  seconds 
beheld  the  spectacle,  the  most  beautiful  and  wonderful  upon  which  the  human  eye 
can  ever  rest.  The  impression  was  overwhelming,  and  so  nearly  blotted  from  my 
memory  all  that  I  had  observed  before  that  I  can  now  recall  it  with  certainty  only 
from  the  written  notes  kept  by  my  assistant;  where  they  are  wanting,  I  can  only  speak 
doubtfully.  Of  course,  from  so  short  a  view  I  could  obtain  but  little  worth  mention- 
ing in  an  official  report,  I  saw  Venus,  Mercury,  Saturn,  and  Regulus.  The  great 


REPORT  OF  PROFESSOR  YOUtfG.  49 

protuberance  on  the  lower  edge  appeared  exactly  like  the  planet  Mars,  and  for  an 
instant  it  was  my  impression  that  it  actually  was  that  planet.  I  mention  this  as  show- 
ing its  color  viewed  by  the  naked  eye.  The  corona  seemed  to  me  nearly  white,  with 
the  slightly  bluish  or  greenish  tinge  of  silver.  As  to  its  form,  my  recollection  is  not 
very  distinct,  but  I  remember  my  surprise  at  the  definiteness  and  irregularity  of  its 
boundary,  for  I  had  expected  an  insensible  gradation  from  the  center  to  the  edges, 
like  that  of  the  zodiacal  light,  for  instance,  and  that  it  would  be  nearly  circular.  It 
was  much  brighter,  also,  than  I  had  looked  for,  and  was  distinctly  visible  on  the  screen 
of  my  spectroscope.  Could  extraneous  light  have  been  excluded,  it  would  have  been 
possible  to  draw  its  outline.  Perhaps  a  good  method  to  secure  accurate  delineation 
of  its  form  at  some  future  eclipse  would  be  to  attach  to  the  eye-piece  of  a  large  tele- 
scope with  low  magnifying  power  a  screen  properly  shaded,  forming  a  sort  of  camera 
obscura.  Upon  this  screen,  with  a  pencil  made  visible  in  the  darkness  by  rubbing  it 
over  with  phosphoric  oil  or  by  some  similar  contrivance,  the  observer  could  sketch  the 
outlines  with  accuracy.  Outlines  thus  drawn  and  compared  with  photographs  would 
settle  decisively  the  question  whether  there  is  really  the  great  difference  supposed 
between  the  actinic  and  the  visible  corona 

LAST   CONTACT. 

A  few  minutes  before  the  end  of  the  eclipse,  I  exchanged  the  eye-piece  before 
used  in  the  comet-seeker  for  a  solar  eye-piece,  magnifying  about  25  times,  and 
observed  the  last  contact  in  the  ordinary  method.  By  some  means,  however,  my  con- 
nection with  the  chronograph  had  been  disarranged,  and  the  observation  failed  to  be 
recorded. 

COINCIDENCES  "BETWEEN  THE  SPECTRUM  OF  THE  CORONA  AND  THAT  OF  THE  AURORA 

BOREALIS. 

On  returning  from  Burlington,  I  found  awaiting  me  the  July  number  of  Silliman'e 
Journal,  in  which  are  given  the  places  of  five  bright  lines,  observed  by  Professor  Win- 
Jock,  in  the  spectrum  of  the  aurora  borealis,  as  follows,  in  numbers  of  Huggins's  scales  : 
"  1 280  brightest,  1 400, 1 5 50, 1 680,  and  2640."  Reduced  to  KirchhofFs  scale,  the  three  first 
would  stand  1247,  1351,  and  1475,  using,  for  the  comparison  of  the  scales,  the  data 
given  by  Professor  Gibbs,  in  his  paper,  upon  "Wave  lengths  by  the  method  of  com- 
parison." If  these  measures  are  correct,  and  I  know  no  reason  to  doubt  them,  though, 
on  account  of  the  faintness  and  evanescence  of  the  lines,  except  the  first,  I  have  not 
been  able  to  verify  them  in  the  auroras  of  the  past  season,  and  have  even  seen  them 
but  three  times,  and  then  only  for  a  few  moments,  we  have  the  following  remarkable 
coincidence:  I  found  in  the  corona  spectrum,  1250^=  20,  1350  ±  20,  and  1474;  in 
the  aurora,  we  have  1247,  1351,  and  1475.  On  the  first  two  coincidences  but  little 
stress  should  be  laid,  as  the  positions  of  the  corona  lines  are  mere  estimations  ;  but  1474 
is  perfectly  well  known,  being  the  reversal  of  a  dark  line  of  the  solar  spectrum,  which 
is  given  by  both  Kirchhoff  and  Thalen  as  belonging  to  Iron,  (not  by  Huggins,  who, 
however,  omits  many  faint  lines ;)  and  its  coincidence,  though  but  with  one  of  the 


7   E   S 


50  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

fainter  lines  of  our  aurora  borealis,  gives,  I  think,  considerable  probability  to  the  con- 
jecture that  the  aurora  borealis  and  the  solar  corona  are  closely  related,  if  not  identical 
phenomena.  The  fact  that  Angstrom  has  detected  the  principal  aurora  line  (1280 
Huggins)  in  the  spectrum  of  the  zodiacal  lig'ht,  points,  to  my  mind,  in  the  same  direc- 
tion, as  showing  that  the  principal  seat  of  the  auroral  light  is  in  a  gas  which  has  cos- 
mical  relations,  and  is  not  solely  terrestrial  — ,  an  atmosphere  above  our  air  of  oxygen 
and  nitrogen,  and  indefinitely  more  rare. 

Upon  Plate  III,  figure  1,  which  exhibits  the  bright  lines  observed  by  me,  I  have 
written  the  numbers  of  certain  of  the  dark  lines  according  to  Huggins's  scale,  while 
the  scale  of  construction  is  that  of  Kirchhoff.  This  renders  the  comparison  of  the  two 
scales  very  easy  to  the  eye. 

RESULTS. 

To  recapitulate  :  The  results  of  my  observations  were  briefly  these : 

FIRST,  positively  and  certainly — 

a)  The  determination  of  the  instant  of  contact  by  a  new  method. 

6)  The  observation  of  the  following  nine  bright  lines  in  the  spectrum,  viz,  C,  D3, 
1250  ±  20,  1350  ±  20,  1474,  F,  2602  i  3,  (2585  i  3  1)  2796  and  h,  of  which  two  are 
entirely  new. 

SECOND,  more  or  less  probably  but  not  certainly — 

a)  The  determination  that  1474,  and  probably,  also,  the  two  fainter  lines  between 
it  and  D3,  belong  to  the  spectrum  of  the  corona. 

6)  The  identification  of  these  lines  with  certain  lines  in  the  spectrum  of  the  aurora 
borealis. 

c)  The  polarization  of  the  light  of  the  faint,  continuous  spectrum  in  a  plane  pass- 
ing through  the  sun's  center.  (This  is  very  doubtful.) 

THIRD,  negatively — 

a)  There  was  no  evidence  obtained  of  a  lunar  atmosphere. 

6)  No  differences  were  observed  between  the  spectra  of  the  different  prominences. 
Very  little  weight  should  be  given  to  this,  however,  as,  from  the  construction  of  my 
instrument  and  the  shoiiness  of  the  time  at  command,  only  different  portions  of  the 
spectrum  were  observed  with  the  different  prominences. 

c)  I  saw  nothing  of  the  "layer  giving  a  continuous  spectrum,"  reported  by 
Secchi,  and  am  confident  that  if  it  exists  it  must  be  exceedingly  thin. 

d)  I  saw  no  trace  of  dark  lines  in  the  faint,  continuous  spectrum  from  the  corona. 
I  ought  not  to  conclude  this  report  without  putting  on  record  my  obligations  to 

my  assistant,  Mr.  Emerson,  whose  presence  of  mind,  fidelity,  good  judgment,  and 
steady  hand  were  invaluable  to  me.  Allow  me  to  mention,  also,  Mr.  Lewis  Boss,  of 
the  present  senior  class  in  Dartmouth  College,  who.  during  the  summer,  was  my 
enthusiastic  and  indefatigable  assistant  in  the  preliminary  measurements  which  were 
necessary  to  determine  the  relations  between  the  scale  of  my  spectroscope  and  that 
of  Kirchhoff,  and  the  other  observations  by  which  I  became  accustomed  to  the  man- 
agement of  the  instrument. 


REPORT  OF  PROFESSOR  YOUNG.  51 

Left  at  Hanover,  in  charge  of  the  Shattuck  Observatory,  he  made  the  observa- 
tions upon  the  eclipse  which  I  take  the  liberty  to  append  as  a  supplement  to  this 
report,  and  for  whose  accuracy  I  will  vouch. 

Very  respectfully,  yours, 

C.  A.  YOUNG. 
Prof.  J.  H.  C.  COFFIN, 

Super  intendi'iit  of  the  American  Nautical  Almanac. 

NOTE. — Although  the  progress  of  science  siuce  this  report  was  prepared,  while  confirming 
most  of  the  results  above  stated,  has  invalidated  others,  and  notably  the  speculation  as  to  the 
identity  of  the  spectra  of  the  Corona,  the  Aurora  Borealis,  and  the  Zodiacal  Light,  it  is  thought 
only  right  that  it  should  stand  as  written.  Accordingly,  in  revising  the  proofs  for  printing,  no 
alterations  have  been  made,  except  a  few  verbal  corrections  of  no  importance  to  the  sense. 

0.  A.  Y. 

PEINCETON,  September,  1877. 


SUPPLEMENT. 


Observations  on  the  eclipse  of  August  7,  1869.  made  at  the  Shattuck  Observatory,  Hanover 

N.  H.     By  Lewis  Boss,  assistant. 

The  instrument  used  was  the  equatorial,  6.4  inches  aperture,  8  feet  8  inches  focal 
length.     Aperture  reduced  to  2 £  inches  ;  power,  127. 


The  "numbers"  of  the  spots  were  determined  by  the  order  of  their  occultation. 
The  accompanying  diagram,  roughly  mapped  from  memory,  will  assist  in  their  iden- 
tification. 

First  contact,  Hanover  mean  time  (all  corrections  applied),  5''  14"'  57". 

Spot  No.  i. 

(North  12°  west  .58  of  sun's  diameter  from  center  of  disc.) 

h.  m.       s. 

Contact  with  penumbra S32     6.5 

Contact  with  nucleus 5  32    H-5 

Nucleus  eclipsed 5  32   25-° 

Re-appearance  of  nucleus -•     6  27  49.0 

Re-appearance  of  penumbra . . 


52  ECLIPSE  OF  THE  SUN,  AUGUST  7,  18G9. 

Small  spot  No.  2. 
(South  40°  west  .40  of  sun's  diameter  from  center  of  disc.) 

h.  m.       s. 
Eclipsed  .  5  52  35.5 


No.  3,  (first  in  group.) 
(North  .09  of  sun's  diameter  from  center  of  disc.) 

First  contact  ......................................  5  56  1  9.0 

Eclipsed  '.  ......................................  ___  5   56  29.0 

Re-appearance  ...............  .....................  642  21.5 

Entirely  clear  of  moon's  limb. 

Spot  No.  4,  (last  in  group.) 
(East  .09  of  sun's  diameter  from  center  of  disc.) 

Eclipsed  .  5   59   10.5 

Re-appearance  ....................................     6  44  33.0 

Entirely  clear  of  moon's  limb. 

Spot  No.  5. 
(South  40°  east  from  center,  distant  from  limb  .1  of  sun's  diameter.) 

First  contact  .......................................     6   13  50.2 

Eclipsed  ..........................................     6   14     o.o 

First  re-appearance  .................................     6  54   15.5 

Complete  emersion  ..................................     6  54  26.5 

Sun  set  eclipsed,  apparently,  about  2\  minutes  before  last  contact.     Sky  mainly 
clear.     Flying  clouds.     Wind  northwest. 

C.  A.  Y, 


EEPOET 


OF 


Miss   MARIA    MITCHELL 


,    IOWA.. 


53 


REPORT  OF  MISS  MITCHELL 


BURLINGTON,  IOWA. 

Observations  of  solar  eclipse  of  August  7,  1869,  at  Burlington,  loiva. 

Station:  The  grounds  of  the  Burlington  Collegiate  Institute,  1514  feetzz  14". 95 
north,  and  1596  feet=  I8.52  west,  of  the  Coast  Survey  Station. 

Instrument:  Telescope  by  Dollond.  Aperture,  4  inches,  reduced  to  \y2  inches  by 
paper  cover;  equatorially  mounted;  moved  by  tangent  screw,  which  worked  imper- 
fectly. The  power  used  was  about  56.*  Colored  glass,  orange-yellow. 

Chronometer:   (Negus,   1293)   slow  of  Burlington   (Coast   Survey)   mean   time, 

5h48m5i8.3  (P-  12). 

The  time  was  counted  aloud  by  Miss  Starke. 

BY    CHRONOMETER 

Eclipse  began ioh    7m  24s. 

Totality  began , 1 1      8  47  .9. 

Totality  ended 1 1    1 1  35  .8. 

Eclipse  ended  .  -. 12     7  40  . 

Moon's  limb  seemed  to  touch  small  spot 10  30  48  .5. 

Moon's  limb  seemed  to  touch  penumbra  of  large  spot 1031  38  .5. 

Moon's  limb  seemed  to  touch  edge  of  nucleus 1032      4. 

Moon's  limb  seemed  to  touch  second  edge  of  nucleus 10   32  38. 

Spot  disappeared 10  32  44  .5. 

The  times  of  passing  off  were  lost. 

The  moon's  limb  was  plainly  uneven,  and  there  was  a  deeper  indentation  a  little 
below  this  spot. 

The  penumbra  of  this  spot  became  paler  as  the  moon's  limb  approached  it,  while 
the  nucleus  of  the  spot  seemed  to  grow  darker,  but  did  not  become  as  dark  as  the  moon. 

The  penumbra  at  the  right  of  the  spot  was  lost  by  paling  out. 

Near  the  limb  of  the  moon  was  a  narrow  bordering  of  light,  and  the  extremities 
of  the  cusps  seemed  still  brighter.  I  changed  the  color  of  the  glass  to  red,  but  still 
saw  this. 

I  changed  back  again  to  the  yellow-orange  glass  before  totality. 

*  I  liad  intended  to  use  a  lower  power,  but  did  not  find  it  in  the  box. 


56  ECLIPSE  OP  THE  SUN,  AUGUST  7,  1869. 

As  totality  approached,  perhaps  two  or  three  seconds  before  the  time  recorded, 
the  limb  of  the  sun  seemed  to  break  up  into  lines  and  points. 

I  have  no  reason  to  think  the  glass  out  of  focus,  and  I  was  not  expecting  any 
such  appearance. 

I  had  intended  to  revolve  the  circle  of  differently  colored  glasses  as  totality  came 
on,  but  finding  it  slide  with  some  difficulty,  I  removed  the  colored  glasses  entirely 
While  doing  this,  I  glanced  at  the  corona.  It  was  of  a  dull,  smoky  white,  not  uniform 
around  the  sun.  There  were  long  rays. 

On  looking  through  the  glass,  I  perceived  two  rosy  protuberances*  on  the  right, 
spirally-shaped.  They  resembled  the  whorl  of  a  half-blown  morning  glory.  They 
were  not  of  one  color,  but  mingled  white  and  pink.  I  had  no  means  of  measuring 
size,  but  estimated  them  as  three  times  that  of  the  spot.  As  I  turned  my  glance  from 
them,  I  saw  on  the  left  of  the  vertex  (inverting  telescope)  another, f  much  larger,  hive- 
shaped,  irregular  in  outline,  undulated,  much  like  heaped-up  cumulus  clouds.  The 
color  of  this  was  also  a  mingling  of  rose-color  and  white.  In  my  rough  notes  I  use 
the  word  "mottled."  As  I  looked  at  this,  I  thought  I  saw  changes  in  itself  which 
were  not  the  result  of  the  moon's  motion.  Upon  reflection,  I  am  doubtful  about  it; 
but  I  received  an  impression  of  the  motion  of  sea-waves. 

Two  other  rosy  prominences  J  sprang  up  on  the  left,  sharply  pointed  and  spread- 
ing at  the  base.  These  were  rose-colored  (pink  and  not  red  rose),  white,  and  violet. 

A  sixth  protuberance  §  began  on  the  left,  which  I  called  "arrow-shaped"  in  my 
first  notes,  and  near  this  the  sun  burst  forth. 

While  watching  these  rosy  points,  I  was  twice  disturbed  by  what  seemed  to  be  a 
flickering  of  light  on  the  moon's  surface  near  its  center. 

Just  before  the  total  phase,  mists  seemed  to  rise,  and  it  seemed  to  grow  hazy 
around  the  sun. 

The  darkness  was  at  no  time  so  great  that  print  could  not  be  read.  My  assistant 
used  a  candle  for  the  chronometer,  but  is  not  sure  that  it  was  necessary. 

In  passing  off,  the  moon's  limb  was  less  rugged,  and  I  did  not  see  the  bordering 
of  brighter  light  until  near  the  end  of  the  eclipse. 

MARIA  MITCHELL. 


Miss  Whitney's  notes. 

Sun's  cusps  definitely  cut. 

Upon  instant  of  totality  the  corona  seemed  to  burst  forth,  irregular  and  cloud-like, 
with  a  soft  light. 

Protuberance  at  vertex  brilliant  and  rounded,  immediately  followed  by  two  others 
45°  to  the  east,  rapidly  increasing  in  size;  then  another,  not  so  rounded  in  appearance, 
about  90°  from  first,  and  along  this  arc,  almost  immediately,  the  sun  appeared. 

"Probably  6  and  7  of  Mayer's  diagram,  Plate  X,  Fig.  I. 

t  Probably  8  of  Mayer's  diagram. 

t  Probably  9  and  10  of  Mayer's  diagram. 

$  Probably  n  of  Mayor's  diagram,  C. 


EEPORT  OF  MISS  MITCHELL.  57 

The  corona  was  prolonged  in  different  directions,  not  evenly  distributed. 
Moon's  edge  in  passing  off  not  so  rough  as  the  other. 
Telescope  by  Alvan  Clark ;   3  inches  aperture. 

Eclipse  began,  3''  56"'  2O8.5;  known  to  be  late. 
Eclipse  ended,  5    56     28  . 

Time  by  watch  compared  immediately  before  eclipse  with  chronometer,  and  set 
to  Burlington  time. 


Miss  Blatdihijs  notes. 

Station:  Roof  of  college  building. 

No  instrument. 

4h  52"'. — Mississippi  of  a  leaden  color;  geese  cackle  and  run  about;  the  land- 
scape has  a  green  tinge;  the  sky  a  lavender  color. 

4h  55"'. — Trees  almost  distinguished;  sun  visible  to  naked  eye  without  pain; 
darkness  about  equal  to  that  of  a  cloudy  moonlight  night;  sky  yellow. 

4h  59'"- — The  horizon  all  around  lighter  than  the  rest  of  the  sky;  birds  fly  to  the 
bell -tower  and  flutter  about;  cries  of  birds  heard. 

5''. — Twinkling  light  upon  the  leaves  of  the  trees;  pale-pink  light  at  the  west; 
painful  cry  of  birds. 


3" 

4 
4 
4 
4 


Miss  Coffins  notes  of  thermometer. 
47™                                               7Q°                 S11        lm- 

68° 

7C                   c        27    . 

72 

4c                                                     71    c                c        42 

76 

c-j                                                     70                    ^        ^7 

/  " 
74 

Oo    •                                                 /  w                    jo/ 

/T- 

,tion  of  totality,  2m  45*. 

Miss  Ely's  notes. 

Station:  Roof  of  Mr.  Foote's  house. 
No  instrument. 

4h  1 5m.  Shadows  lengthen;  a  flock  of  geese  fly  home;  general  appearance  of  land- 
scape as  before  a  thunder-storm. 

4h  30™.  College  building  not  distinctly  seen  on  account  of  smoke. 
4b  40™.  Swallows  fly  home. 
4h  45™.  Venus  and  Mercury  seen. 
8  E  s 


58  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

4''  56™.  Arcturus  and  Saturn  are  seen.  Broad  bands  of  yellow  and  red  color 
appear  around  the  horizon.  Corona  seen.  A  band  of  blood-red  color  above  the  sun, 
and  two  small  bright  points  are  visible,  one  below  and  the  other  at  the  right  of  the 
moon's  disk. 

A  bluish  light  pervades  the  landscape.  As  total  phase  ends,  the  bands  about 
the  horizon  change  to  purple  and  blue. 


Miss  Carter's    notes. 
(With  binocular  glass  and  photometer.) 

Measurement  of  light  by  photometer  showed  a  gradual  decrease  of  illumination 
until  4b  30™,  when  the  light  waned  very  rapidly  and  could  not  be  seen  at  4''  56'". 

4h  56™,  Corona  formed  of  irregular  yellowish  rays,  with  two  ruby-colored  leaf- 
shaped  flames.  Blood-red  band  of  light  at  the  right,  above.  Dark  body  of  moon 
sharply  defined  and  of  greenish  tint. 

5b  25™  30".  Venus  still  visible  to  the  naked  eye. 


Miss  Reynold's  notes. 
(Dollond  glass,  2\  inches.) 

Body  of  moon  of  inky  blackness.     Cusps' sharply  defined. 
The  light  did  not  appear  like  ordinary  sunlight  diminished. 
4h  54™.  Venus  seen. 

During  totality  two  intensely  bright  lines  were  seen  across  the  corona  to  moon's 
disk,  one  from  the  right  and  one  from  below,  as  seen  by  the  naked  eye. 
Fire-flies  seen.     Birds  flew  around  as  if  lost.     Crickets  chirped. 


Miss  Glasier's  notes. 
(Glass  by  Clark,  3  inches.) 

Sphericity  of  both  moon  and  sun  very  evident. 

At  total  phase  I  was  surprised  at  the  irregularity  of  corona;  not  clearly  defined 
against  background  of  sky.  Rays  of  light  thrown  over  moon. 

Light  on  terrestrial  objects  decidedly  greenish;  not  half  black,  as  in  thunder- 
storms. 

I  read  writing  with  a  moderately  black  pencil  easily  at  totality.  Protuberances 
not  rose  but  flame  colored. 


REPORTS 


MR.  JOHN  N.  STOCKWELL  AND  PROF.  D.  G.  EATON. 


,    IOWA.. 


REPORT  OF  J.   N.   STOCKWELL. 


BURLINGTON,  IOWA. 

* 

DEAR  SIR  :  In  conformity  with  your  request,  I  herewith  submit  a  brief  account 
of  the  solar  eclipse  of  August  7,  as  it  appeared  to  me,  at  Burlington,  Iowa.  As  I 
placed  myself  on  the  line  of  totality  merely  for  the  purpose  of  witnessing  a  total 
eclipse,  regarded  as  a  wonderful  celestial  show,  rather  than  for  the  purpose  of  making 
valuable  scientific  observations,  rny  outfit  corresponded  in  simplicity  with  the  design 
of  my  journey.  The  only  optical  appliances  at  my  service  consisted  of  a  single 
unmounted  achromatic  telescope  of  25  inches  focal  length  and  2  inches  clear  aper- 
ture, with  a  magnifying  power  of  about  forty-five  times.  This  instrument  gave  a  very 
sharply  defined  image  of  the  sun's  limb,  and  also  of  the  spots  on  his  surface.  I  con- 
trived a  very  simple  wooden  mounting  for  the  telescope,  which  steadied  it  sufficiently 
for  the  purpose  of  observing  the  times  of  contact  and  the  various  other  attendant 
phenomena  of  the  eclipse. 

The  observed  times  of  the  different  contacts  are  as  follows: 

Beginning  of  eclipse 1 2h  50^  9" 

Beginning  of  total  eclipse 13  51  42 

End  of  total  eclipse 13  54  30 

End  of  eclipse 14  50  42 

It  should  be  observed  that  the  times  here  given  are  the  chronometer  times  as 
counted  to  the  party.  (Chro.  Hutton,  202,  p.  20.) 

During  the  progress  of  the  eclipse  I  noted  the  time  of  the  occultation  of  the  large 
spot  as  1 4b  1 5m  1 38.  No  other  phenomena  were  noted  till  near  the  time  of  totality,  when 
my  attention  was  drawn  to  a  very  bright  red  spot,*  situated  very  nearly  in  the  lower 
limb  of  the  moon,  and  apparently  considerably  within  the  circumference  of  its  disk, 
and  also  extending  a  considerable  distance  beyond  the  border  of  the  moon  into  space: 
bvit  the  outline  of  a  perfect  limb  of  the  moon  was  distinctly  visible.  It  seemed  as  if 
this  spot  was  formed  by  the  sun  shining  through  a  very  large  hole  through  the  moon, 
or  perhaps  the  phenomenon  might  be  more  appropriately  likened  to  the  sun  shining 
•through  a  tremendous  chasm  in  the  body  of  the  moon  with  a  magnificent  arch  span- 
ning it  from  side  to  side  and  filling  up  the  gap  in  its  surface.  The  depth  I  should 
estimate  as  at  least  equal  to  one-twentieth  of  the  moon's  diameter;  and  were  it  not 
for  the  exceeding  wildness  of  the  idea,  when  we  reduce  such  estimates  to  linear  meas- 
ures, I  should  be  inclined  to  estimate  it  as  3  per  cent,  greater,  or  at  one-fifteenth 
of  the  moon's  diameter!  As  soon  as  I  recovered  from  the  surprise  occasioned  by  the 

•Probably  No.  8  of  Professor  Mayer's  diagram,  Plate  X,  Fig.  1.    C. 

61 


62  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

imposing  grandeur  and  magnificence  of  the  spectacle  I  removed  the  red-screen  glass 
from  the  telescope,  and  what  was  before  the  bright-red  spot  was  changed  to  a  mag- 
nificent rose-colored  cloud  or  protuberance,  having  apparently  the  same  form  and 
dimensions. 

When  the  eclipse  became  total  another  large  rose-colored  protuberance*  appeared 
at  about  a  quarter  of  the.  circumference  of  the  moon's  disk,  from  the  first  spot,  towards 
the  western  limb.  This  spot  continued  to  increase  in  magnitude  and  brilliancy  while 
the  totality  lasted,  and  in  the  mean  time  several  smaller  spots  of  a  similar  nature 
appeared  between  the  two  which  have  just  been  mentioned.  Three-quarters  of  the 
moon's  circumference  was  entirely  barren  of  these  rose-colored  protuberances,  and 
also  of  all  other  phenomena  of  especial  interest.  As  soon  as  the  totality  ceased  and 
a  slender  crescent  of  the  solar  disk  appeared  on  the  western  limb  of  the  moon,  these 
smaller  protuberances  disappeared,  but  not  instantaneously,  there  being  an  appreciable 
interval  before  they  were  wholly  obliterated.  The  upper  protuberance  was  visible 
several  seconds  after  the  eclipse  ceased  to  be  total.  But  the  large  rose-colored 
protuberance  at  the  lower  limb  of  the  moon  remained  the  most  conspicuous  local 
phenomenon  during  the  total  phase.  It  also  remained  visible  for  some  seconds  after  the 
solar  crescent  had  extended  itself  beyond  the  "hole  in  the  moon,"  which  permitted 
this  rose-colored  cloud  to  be  both  a  protuberance  and  an  indentation,  although  the 
two  parts  were  apparently  separated  by  a  shadowy  outline  of  the  lunar  disk. 

In  regard  to  the  corona,  I  can  only  observe  that  I  did  not  concentrate  my  attention 
upon  it  to  any  great  extent.  Its  color  I  noticed  to  be  a  pure  white  throughout  its 
whole  extent,  and  its  average  breadth  was  about  one-half  the  apparent  radius  of  the 
moon.  The  outer  circumference  of  the  corona  was  considerably  distorted;  its  shape 
somewhat  resembled  that  of  an  elastic  hoop  which  had  been  subjected  to  pressure  from 
the  outside  at  several  different  points,  producing  concavities  at  the  places  where  the 
pressure  was  applied,  and  angular  points  midway  between  them. 

The  color  of  the  moon  I  called  a  dark  slate,  instead  of  a  jet  black,  as  it  is 
sometimes  said  to  be  on  such  occasions.  It  was  also  sensibly  uniform  throughout  its 
whole  extent.  The  darkness  was  not  as  great  as  I  had  anticipated,  but  I  found  some 
difficulty  in  taking  notes  during  the  totality.  The  planets  M ercnry  and  Venus,  as  well 
as  several  of  the  fixed  stars,  were  plainly  visible.  The  darkness  somewhat  exceeded 
that  at  the  time  of  the  full  moon,  but  the  color  of  the  sky  was  unlike  both  that  of 
night  and  of  twilight.  The  sky  was  also  sensibly  darker  in  the  vicinity  of  the  sun 
than  it  was  near  the  horizon.  The  belt  of  darkness  also  extended  much  farther  from 
east  to  west  along  the  ecliptic  than  from  north  to  south. 

I  have  thus  very  briefly  stated  the  main  features  of  the  eclipse  as  they  presented 
themselves  to  me,  and  I  submit  them  for  what  they  may  be  worth  in  the  discussion  of 
those  problems  relating  to  the  physical  constitutions  of  the  sun  and  moon. 
Very  respectfully,  yours, 

JOHN  N.  STOCKWELL. 

Prof.  J.  H.  C.  COFFIN, 

Superintendent  American  Ephemeris,  and  Chief  of  Burlington  Eclipse  Party. 
(Communicated  September  27,  1869.) 

"Probably  No.  11  of  Mayer's  diagram.     C. 


REPORT  OF  PROF.  D.  G.  EATON. 


BURLINGTON,  IOWA. 

BROOKLYN,  N.  Y.,  September  14,  1869. 

DEAR  SIR  :  Yours  of  the  i  ith  instant  is  just  received,  and  I  hasten  to  reply.  My 
observations  on  the  late  eclipse  were  made,  as  you  may  remember,  with  a  small 
telescope  of  about  2-inch  object  glass,  belonging  to  Professor  Young.  Instead  of 
having  a  solar  eye-piece,  it  was  provided  with  a  frame  carrying  a  white  disk  for 
receiving  the  image  of  the  sun.  During  totality  I  used  only  the  naked  eye.  I  tried 
in  vain  to  view  the  corona  through  the  telescope;  but  in  so  doing,  while  attempting  to 
thrust  my  head  between  the  wires  bearing  the  paper  disk,  I  threw  the  sun  out  of  the 
field,  and  could  not  recover  it  without  too  great  a  sacrifice  of  time.  My  notes  taken 
during  the  eclipse,  and  written  out  soon  afterwards,  are  as  follows  : 

TIMES    OF    CONTACT    BY    THE    CHRONOMETER.       Hutton,   2O2. 

Local  mean  time. 

First  contact 1 2h  50™  1 5"  3h  56™  238.5 

Beginning  of  totality 13    51     41  4   57    39-7 

End  of  totality 13   54    33  5     o    31.2 

Last  contact 14   5°    42  5   56    3 l  -2 

The  first  contact  was  suspected  some  two  or  three  seconds  previous  to  the  time 
above  noted,  but  I  preferred  not  to  record  the  time  until  the  contact  was  so  evident  as 
to  leave  no  room  for  doubt.  The  time  for  the  beginning  of  totality,  I  think,  cannot 
be  more  than  one  second  in  error.  That  for  the  end  of  totality  I  am  not  so  confident 
of,  my  attention  being  so  much  absorbed  by  the  brilliant  star-like  protuberance  near 
the  bottom  of  the  moon's  disk.  I  must  also  confess  to  a  little  excitement  about  that  time. 
Still  I  think  the  time  above  recorded  cannot  be  more  than  one,  or,  at  most,  two  seconds 
in  error. 

The  immersion  of  the  large  spot  was  noted  as  follows  : 

First  contact - 1 3h   H™  39° 

Second  contact 1 3     J  5     2O 

There  seemed  to  be  a  slight  repulsion  between  the  spot  and  moon  at  the  first 
contact,  so  that  the  moon's  edge,  as  it  appeared  on  the  screen,  seemed  indented  by 

63 


64  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

nearly  the  semi-diameter  of  the  spot  before  contact  actually  occurred.  I  did  not  notice 
either  adhesion  or  repulsion  at  the  second  contact.  At  emersion  the  first  contact  was 
not  observed.  The  second  contact  was  14''  9™  27s. 

The  following  notes  were  taken  as  the  eclipse  was  advancing : 

4h  25™  (Burlington  time).     Landscape  darkens. 

4    35    Sky  deepens  its  blue,  especially  overhead. 

4    40    Wind  N.  E.,  lulling. 

4   43    Wind  increasing  again. 

4   45    Sky  intensely  blue  overhead ;  darkness  coming  on. 

4    50    Sky  darkens  rapidly,  but  still  retains  its  blue  color. 

4    53    Appearance  of   an   approaching    thunder    storm,   but    without    clouds, 
lightning,  or  thunder. 

4    56    Dark,  weird  and  ghastly  appearance  of  landscape. 

4    57    Venus  appeared  very  clear  and  bright. 

Venus  appeared  to  others  before  I  saw  it,  and  must  have  been  visible  nearly  two 
minutes  before  totality.  During  totality  I  could  spare  time  for  only  a  single  glance 
around  the  heavens;  during  which  I  recognized  Mercury,  Venus,  Regulus,  Arcturus, 
and  a  Lyra?.  Nothing  peculiar  in  their  color  was  noticed.  I  had  not  time  to  trace 
out  the  sickle,  or  look  for  other  stars  as  I  had  intended.  The  landscape  appeared  of 
an  ashy  or  leaden  darkness.  The  light  I  judged  to  be  not  quite  equal  to  the  full  moon 
at  night.  I  could  not  easily  read  my  penciled  notes;  but  a  friend  told  me  he  could 
read  the  print  of  a  common  newspaper.  The  appearance  of  the  heavens  was  peculiar. 
While  the  stars  were  shining  overhead  a  beautiful  twilight,  tinted  with  the  hues  of 
sunset,  extended  entirely  around  the  horizon. 

The  Baily  beads  were  very  conspicuous.  Just  before  totality  the  thin  crescent 
was  suddenly  broken  up  by  dark  lines  shooting  out  from  and  perpendicular  to  edge 
of  the  moon,  and  transverse  to  the  crescent.  The  parts  thus  separated  from  each 
other  immediately  gathered  up  into  beads  by  an  apparent  mutual  repulsion,  like 
globules  of  water  on  a  dusty  floor.  I  noticed  very  little  if  any  lateral  motion  among 
them.  The  Baily  beads  were  not  seen  at  emersion,  because,  as  before  remarked,  I 
had  thrown  the  sun  out  of  the  field  in  my  effort  to  see  the  corona  through  the  teles- 
cope. The  corona  was  observed  entirely  with  the  naked  eye.  Its  shape  was  irregular. 
At  first,  it  seemed  more  prominent  a  little  to  the  right  of  the  top.  It  changed  its  form 
rapidly,  however,  until  it  approximated  to  a  square  or  rhomboidal  form.  Its  width  was 
not  uniform,  but  I  should  judge  it  would  average  the  radius  of  the  moon,  perhaps 
more.  It  seemed  to  blaze  out  from  behind  the  moon  with  a  beautiful  silver  light,  and 
to  consist  of  bright  rays  upon  a  thin  flame  or  background  of  white  light,  less  intense 
but  more  uniform  in  brightness.  The  rays  were  perfectly  straight  and  seemed  to  pro- 
ceed directly  from  the  centre  of  the  sun.  The  corona  appeared  suddenly,  at  the 
instant  of,  but  not  before,  totality.  It  seemed  to  burst  out  like  a  blaze  of  glory,  and 
was  inexpressibly  beautiful.  I  was  in  a  measure  prepared  for  the  grandeur  and  gloom 
of  the  sky  and  the  landscape,  but  not  at  all  for  the  exquisite  beauty  of  the  corona. 
Its  light  was  peculiar.  It  had  nothing  of  the  dazzling,  blinding  light  of  the  sun,  but 
a  beautiful  silvery  light  all  its  own,  which  was  more  pungent  than  moonlight,  but 


EEPOET  OF  PKOF.  D.  G.  EATON.  65 

which  failed  to  light  up  either  air  or  earth  so  much  as  T  should  expect  from  its  bright- 
ness. I  noticed  two  protuberances  of  great  beauty :  one  about  1 20°  *  from  the  top 
eastward,  and  the  other  about  1 70°  f  from  the  top  westward,  both  of  a  bright  red  color. 
The  one  on  the  east  side  seemed  to  lap  over  or  enter  the  disk  of  the  moon  at  least  one 
digit,  The  one  near  the  bottom  was  the  brightest,  and  shone  with  great  brilliancy, 
emitting  short  rays  in  every  direction,  even  inwards  over  the  edge  of  the  moon.  This 
was  perhaps  the  most  beautiful  object  during  the  entire  period  of  totality.  Two  or 
three  other  protuberances  were  noticed,  but  my  attention  was  so  absorbed  by  these 
two  that  I  did  not  attempt  to  locate  them. 

The  approach  of  the  dark  shadow  from  the  west  could  not  be  observed  because 
the  landscape  in  that  direction  was  hidden  by  intervening  houses.  I  attempted,  how- 
ever, to  catch  a  view  of  the  shadow  in  its  flight  eastward  across  the  prairies  on  the 
opposite  side  of  the  river;  but,  unfortunately,  several  gentlemen  happening  to  stand 
so  as  to  intercept  my  view  in  that  direction,  I  was  compelled  to  change  my  position 
some  ten  feet  or  more,  and  before  this  could  be  done  the  shadow  was  gone.  I  had, 
however,  instructed  my  wife  and  several  friends  to  look  specially  for  the  flight  of  the 
shadow  eastward,  but  none  of  them  were  able  to  see  it. 

The  effect  of  the  whole  scene  on  my  own  mind  was  peculiar,  and  quite  different 
from  my  expectations.  Though  I  felt  myself  in  a  measure  prepared  for  the  scene  by 
a  careful  study  of  the  subject,  and  by  the  descriptions  of  other  eclipses  given  by 
careful  observers,  I  was  completely  surprised,  and  for  a  moment  almost  bewildered. 
The  whole  scene — the  heavens  above  and  the  earth  beneath — had  the  appearance  of 
awful  gloom,  as  if  some  strange  and  fearful  calamity  were  impending.  Just  before 
totality,  as  the  shadow  approached  from  the  west,  an  undefined  horror  seemed 
gathering  in  the  sky — a  cloud,  and  yet  not  a  cloud — a  tornado,  and  yet  only  a  light 
breeze!  All  nature  seemed  to  hesitate,  and  everything  was  a  contradiction.  I  can 
well  understand  how  such  an  event,  not  understood  nor  expected,  would  make  the 
stoutest  heart  quail  and  fill  the  sternest  mind  with  fear  and  dread. 

The  time  was  all  too  short  to  make  the  observations  I  had  intended,  though  I 
think  I  could  do  much  better  another  time.  Never  did  three  minutes  seem  to  pass  so 
quickly;  and  on  the  other  hand,  never  was  so  much  enjoyment  crowded  into  three 
minutes!  I  have  climbed  the  Alps  and  visited  London,  Paris,  and  Rome,  but  I 
would  sooner  lose  the  memory  of  them  all  than  of  those  three  minutes  on  Burlington 
heights. 

On  my  way  home,  I  spent  several  days  at  Indianapolis,  which  was  only  a 
few  miles  outside  of  the  shadow,  and  I  have  the  testimony  of  several  observers  there 
that  the  corona  was  plainly  visible.  If  so,  it  will  have  some  bearing  on  the  question 
whether  the  corona  can  be  seen  before  totality.  Some  five  or  six  intelligent  observers 
(among  whom  were  Rev.  Mr.  Way,  Mrs.  Judge  Roach,  and  Miss  McLean)  all  agree 
that  at  the  time  of  greatest  obscuration,  when  the  crescent  of  the  sun  seemed,  as  they 
expressed  it,  like  a  "mere  pencil  mark,"  the  whole  disk  or  outline  of  the  moon  was 
visible,  and  well  defined  by  the  faint  halo  or  corona  shining  out  from  behind.  If 

*  Probably  No.  6  or  7  of  Mayer's  diagram,  Plate  X,  Fig.  1.    C. 
t  Probably  No.  8  of  Mayer's  diagram,  Plate  X,  Fig.  1.     C. 
9  E   S 


66  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

they  really  saw  the  whole  outline  of  the  moon,  the  corona  must  have  been  visible  to 
some  extent.  At  the  time  of  greatest  obscuration,  they  all  agree  that  the  eclipse 
could  be  viewed  with  the  naked  eye,  and  hence  they  were  not  likely  to  be  deceived 
by  their  smoked  glasses.  Shall  we  receive  their  testimony?  At  Burlington  several 
of  my  friends  who  were  specially  requested  to  notice  the  fact  could  not  see  the 
corona  even  a  second  before  or  after  totality. 
Respectfully,  yours, 

D.  G.  EATON. 
Prof.  J.  H.  C.  COFFIN. 


REPORTS 


OP 


MR.  JOHN  WEISSNER  AND  MR.  E.  P.  AUSTIN. 


67 


FROM  THE  REPORT  OF  MR.  JOHN  WIESSNER. 


[Compiled  by  Professor  COFFIN  and  combined  with  work  of  other  parties.] 
GEOGRAPHICAL    POSITIONS   AND    TIME. 

Mr.  Wiessner  was  detailed  to  make  observations  at  Mount  Pleasant,  Iowa. 
Kewanee,  111.,  and  Monroe,  Mo.,  for  the  geographical  positions  of  those  places,  and  at 
Monroe  to  observe  the  eclipse. 

He  used  for  the  former  a  Gambey  sextant,  with  which  he  was  familiar  from  long 
practice,  and  an  artificial  mercury  horizon.  The  index  correction  of  the  sextant  was 
found  by  repeated  measurements  on  each  day  and  night  when  observations  were  made. 
His  observations  of  the  sun  included  in  each  series  a  nearly  equal  number  of  altitudes 
of  each  limb,  also  an  equal  number  in  each  position  of  the  roof  of  the  horizon.  His 
two  sons,  who  accompanied  him,  noted  the  times  bv  the  chronometers. 

The  observations  of  Professor  Watson  at  Mount  Pleasant,  and  of  Mr.  Austin,  at 
Kewanee,  are  combined  with  those  of  Mr.  Wiessner,  to  complete  the  determination 
of  the  positions  of  those  places. 

MOUNT   PLEASANT,    IOWA, 

is  28  miles  from  Burlington,  on  the  Burlington  and  Missouri  Railway.  The  observa- 
tions were  made  at  the  station  occupied  by  the  parties  of  Professor  Watson  and  Pro- 
fessor Morton,  in  the  Fair  grounds,  about  i^  miles  from  the  railroad  station. 

The  following  are  the  determinations  of  the  latitude: 

1869.  °      ' 

August  7.  By  9  circum-meridian  altitudes  of  the  sun +40  56  59.9 

1 1.  By  1 8  circum-meridian  altitudes  of  the  sun 57   13.0 

10.  By  10  circum-meridian  altitudes  of  a.  Aquila? 57   17.0 

10.  By  1 2  altitudes  of  Polaris 57  27.2 

Mean  of  sun  and  a.  Aquilse 40  57   10.0 

Adopted  value +4°  57   *8.6 


The  observations  on  the  7th  were  made  by  Professor  Watson;  the  rest  by  Mr. 
Wiessner. 

For  the  longitude  we  have: 

By  chronometer  Negus  1074  (see  page  14). 

Reduction  to  Reduction  to  Longitude  from  observations  at  Mount  Pleasant. 

18°9'  Burlington  mean  time.        Mount  Pleasant  mean  time.        Burlington. 

August  10.  5b  ^  +Sh  54m  37"-0     +1"1  448-°       7  P-  m.  alts,  of  sun. 

g    >  +  5h  56™  2i".o  35-7  45-3      14  p.  m.  alts,  of  «Tauri. 

20   )  34-3  46-7     28  a.  m.  alts,  of  sun. 


70  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

By  chronometer  Negus  1304  (see  page  13). 

Observations  at  Mount  Pleasant. 

August  10.  5h     +5h  55-  4^.2     +5h  542  3*.9     +z-  43°.3  ^ 

9  47-3  2  -3  45  -o  >  Same  asforchron.  1074. 

20  47.6  %         1.3  46.3) 

By  chronometer  Negus  1233  (seepage  15). 

August  7.     oh     +6U     2m  4794     +6h     im  38.i      +im448.3     5  p.  m.  alts,  of  sun. 
The  concluded  result  is: 

Mount  Pleasant,  oh     im  45s.o,  west  of  Burlington, 

o    57     58  . 7=14°  2 g'  40",  west  of  Washington. 
6      6     10.8  —  91    32  42,  west  of  Greenwich. 

KEWANEE,    ILLINOIS, 

is  on  the  Chicago,  Burlington  and  Quincy  Railway,  75  miles  northeast  from  Burlington. 
The  observations  were  made  at  the  eclipse  station  of  Mr.  Austin,  in  the  yard  of  Mr. 
A.  Fiirst,  about  5,500  feet,  as  estimated  by  telegraph  poles  and  paces,  or  a  little  more 
than  a  mile,  northeast  from  the  railway  station. 

The  observations  of  Mr.  Wiessner,  July  31   and  August  i,  and  of  Mr.  Austin, 
August  7,  furnish  the  following  results: 

For  latitude  of  the  place  of  observation: 

1869.  o          /          // 

July  31  and  August  i,  by  46  circum-meridian  altitudes  of  sun +41    15   15.8 

July  31,  by  9  circum-meridian  altitudes  of  a.  Ophiuchi 7.7 

August  i,  by  14  circum-meridian  altitudes  of  a  AquilaB 10.9 

,    by  4  circum-meridian  altitudes  of  Jj  Ophiuchi 59.5 

July  3 1,  by  10  altitudes  of  Polaris 34.2 

August  i ,  by  i  2  altitudes  of  Polaris 43-5 

by  4  altitudes  of  /?  Ursse  Minoris 45. 


Mean  by  sun  and  south  stars 14.5 

Mean  by  north  stars 40.  i 

Concluded  latitude 4-41    15    27.3 

For  longitude  : 

By  chronometers  Negus  1074,  1304,  and  i3n  (see  pages  14,  i3,  and  12). 

PI,™  Redaction  to  Reduction  to  Longitude  from 

on-         Burlington  mean  time.  Kewance  mean  time.  Burlington.  Observations  at  Kewanee. 

August  i.  o,  1074  +5"  56     i78.5  +6h     im     28.3    — 4m  44S.8  28  Equal  alts,  of  sun. 
1.0,1304       5     55     42.2        6      o     26.8*  44.6  Comparison  with  1074. 

7.0,1131        5    48     30.8        5     53     15.7  44 .9  56  Equal  alts,  of  sun. 

The  concluded  longitude  is : 

Kewanee,  oh     4m  448.8,  east  of  Burlington, 

o    51     28.9zzi2°52'  13",  west  of  Washington. 
5     59     41.0—89    55    15,  west  of  Greenwich. 

*  Diminished  by  0».3.     See  note  page  13. 


EEPOET  OF  MR.  JOHN  WEISSNER.  7  I 

MONROE,  MISSOURI, 

is  on  the  Hannibal  and  Saint  Joseph  Railway,  30  miles  southwest  from  Quincy,  111- 
The  observations,  both  for  geographical  position  and  of  the  eclipse,  were  made  by  Mr. 
Wiessner  at  the  "Seminary,"  about  one-fourth  of  a  mile  northeast  from  the  railway 
station.  He  estimated  the  elevation  above  mean  water  of  the  Mississippi  River  to  be 
230  feet,  and  above  the  sea  600  feet. 

His  observations  furnish  the  following-  results: 

For  latitude  of  the  place  of  observation. 
1869.  °      '      " 

August  6.  By  26  circum-meridian  altitudes  of  sun +39  39   1 2-5 

7-  By  35  circum-meridian  altitudes  of  sun 39   1 1.4 

8.  By  2 1  circum-meridian  altitudes  of  sun 39  34.2 

5.  By  4  circum-meridian  altitudes  of  a  Ophiuchi 38  37.5 

7.  By  1 7  circum-meridian  altitudes  of  a  Aquilre 38  33.0 

August  5.  By  6  altitudes  of  Polaris 39  2 1.8 

7    By  14  altitudes  of  Polaris 39  31.2 

Mean  from  sun  and  south  stars +39  39     6.4 

Mean  from  Polaris +39  39  26.5 

Concluded  latitude +39  39   J  6.5 

For  longitude: 

By  chronometers  Negus  1074  and  1304  (see  pages  14  and  13). 

fi,™  Reduction  to  Reduction  to  Longitude  from  rn,aorr»tinn«  at  Mnnmo 

Chron.        Burlington  mean  time.  Monroe  mean  time.  Burlington. 

August  6.  ob  1074  +5h  56m  i88.2  +5h  53™  458.8  +2m  3284     16  Equal  alts,  of  sun. 

7.0  18.7  46.5  32.2     91  Equal  alts,  of  sun. 

8.  o                              19.3                    47-8  31 -5     2 1  Equal  alts,  of  sun. 
August  6.  oh  1304  +5h  55'"  449-7  +5h  53m   i28.2  +2m  328.5*  Comparisons  with  1074. 

7.  o  45  .o  12 .8  32 .2* 

8.0  45.6  14.2  31.4* 

The  concluded  longitude  is: 

Monroe,    oh     2m  328.o,  west  of  Burlington, 

o    58     45.7=14°  41'  26",  west  of  Washington. 

6      6     57.8  —  91  44    28,  west  of  Greenwich. 

Observations  of  tJie  Solar  Eclipse,  August  7,  1 869. 

The  eclipse  was  observed  by  Mr.  Wiessner,  at  Monroe,  with  a  dialytic  telescope 
by  Pfossl,  belonging  to  the  United  States  Naval  Academy;  equatorially  mounted;  3 
inches  aperture,  and  37  inches  focal  length,  and  magnifying  power  61.  It  was  placed 
in  a  window  on  the  first  floor  and  in  the  west  front  of  the  Seminary,  whose  geographical 
position  is  given  above.  A  dark-red  shade  glass  was  used  for  the  beginning  and  end 
of  the  eclipse,  a  light-red  glass  for  the  totality.  The  times  of  the  several  phases  were 
noted  by  his  two  sons.  During  the  total  obscuration  "the  seconds  of  the  chronometer 
were  made  visible  by  candle-light  at  a  distance  of  2  feet,  but  hardly  plain  enough." 

*  Diminished  by  O1..-.     See  note  p.  13. 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


Mr.  Wiessner  thinks  that  in  the  obscurity  both  of  his  assistants  noted  the  times  of  the 
sun's  reappearance  by  the  wrong  end  of  the  second-hand,  and  30"  too  much.  They 
are  given,  however,  as  originally  noted. 

The  chronometer  corrections  referred  to  Monroe  mean  time,  obtained  from  the 
tables  on  pages  13  and  14  and  the  longitude  from  Burlington,  on  page  71,  are 

August  7,  5h+  5h  53'"  46.8"  for  Negus  1074. 
+  5     53     13-°   for  Nef/us  1 304. 


By  chronometer,  1074. 

By  chronometer,  1304.             Predicted 

Chronometer 

Monroe  mean 

Chronometer 

Monroe  mean 

American 

time. 

time. 

time. 

time. 

Ephemeris. 

h.  m.  s. 

h.  m.  s. 

h.  m.  s. 

h.  m.  s. 

h.  m.  s. 

Beginning  of  eclipse. 

10    I     II 

3  54  57-8 

10   I  46.  8 

3  54  59-  8 

3  55  4-  86 

Beginning  of  totality. 

ii  3  57-5 

4  57  44-3     :      ii  4  3i-5 

4  57  44-  5      4  58  4"-  13 

End  of  totality 

1  1  5  24.  8 

4    CO     I  I     6 

ii    <;   14  8 

4.    5Q      78        •*    cK   At)    11 

End  of  eclipse 

12    I    58.8 

5  55  45'  6 

12  2  31.3 

5  55  44-  3 

5  55  48.09 

The  sky  appeared  perfectly  clear  during  the  entire  day.  The  following  notes 
were  made  of  an  aneroid  barometer  and  thermometer,  the  former  corrected  — 0.20  inch 
by  comparison  with  the  barometer  used  at  the  eclipse  station  in  Burlington. 


Bar-          Ther- 
ometer.     luometer. 
in. 


Ql/2 

n  a.  m. 

29.74 

74' 

2 

p.  m. 

.60 

80 

3 

p.  m. 

.62 

78 

5 

p.m. 

•57 

78 

5 

p.  m. 

•57 

77 

August  7, 


Just  before  totality. 
Just  after  totality. 

Mr.  Wiessner  speaks  of  the  breaking  up  of  the  crescent  just  before  the  total 
obscuration  as  presenting  the  appearance  of  "pearls  moving  from  left  to  right." 

During  the  total  obscuration,  Venus  and  Mercury  were  visible.  The  corona 
appeared  to  the  naked  eye  more  extended  on  the  southeast  limb.  The  prominences 
noticed  were  of  a  reddish  color. 

J.  H.  C.  COFFIN 


REPORT  OF  MR.  E.  P.  AUSTIN. 


KEWANEE,  ILLINOIS. 

CAMBRIDGE,  MASS.,  September  14,  1869. 

SIR  :  I  have  the  honor  to  submit  the  following  report  of  operations  at  Kewanee, 
111.,  to  determine  the  longitude  and  observe  the  total  eclipse  of  the  sun  of  August  7, 
1869. 

I  left  Burlington  at  10  a.  m.  on  Thursday,  August  5,  accompanied  by  Mr.  A.  L. 
Covert.  The  instruments  consisted  of  a  mean-time  chronometer,  Negus  1311,  a  sex- 
tant by  Gambey,  and  an  artificial  horizon  of  mercury,  a  binocular  Navy  glass  magnify- 
ing about  four  diameters,  furnished  with  colored-glass  shades,  and  a  telescope  by  Mr. 
Alvan  Clark,  with  aperture  of  3  inches  and  focal  length  48  inches. 

We  arrived  at  Kewanee  about  2  p.  in.,  and  set  out  immediately  to  find  the  station 
previously  selected  by  Mr.  Wiessuer,  which  is  situated  on  the  farm  of  Mr.  August 
Fiirst,  about  three-fourths  of  a  mile  north-northeast*  from  Kewanee  Railroad  depot, 
on  a  north  and  south  road. 

The  weather  had  been  cloudy  all  day,  with  occasional  drops  of  rain,  and  con- 
tinued until  night;  during  the  night  some  rain  fell. 

On  the  morning  of  the  6th,  about  9  o'clock,  the  clouds  broke  away  slightly,  so  as. 
to  give  occasional  glimpses  of  the  sun,  and  I  endeavored  to  take  some  double  altitudes 
of  the  sun  in  hopes  that  the  weather  would  clear  in  the  afternoon;  but  soon  after  10  a.  m. 
it  clouded  up  entirely  and  began  to  rain  and  rained  with  very  little  intermission  till 
about  4  p.  m.,  and  at  intervals  till  6.  In  the  evening  I  went  down  to  the  telegraph 
office  pursuant  to  arrangements  to  compare  chronometers  and  interchange  signals  with 
Burlington. 

The  weather  remained  cloudy,  but  with  some  signs  of  breaking  away,  and  about 
half  past  9  there  were  some  stars  visible,  but  by  the  time  I  had  reached  the  station 
the  sky  was  completely  overcast. 

On  looking  out,  however,  some  twenty  minutes  later,  I  was  surprised  to  find  it 
had  cleared  off  almost  entirely,  and  I  decided  to  try  to  get  some  observations  of  stars 
for  time.  On  attempting  to  observe  it  was  found  that  the  moisture  in  the  atmosphere 
condensed  so  rapidly  on  the  glass  shade  of  the  artificial  horizon  as  to  render  it  impos- 
sible to  see  the  stars 

On  the  morning  of  the  7th  there  was  a  cloudless  sky,  and  the  atmosphere  had 
been  purified  by  the  heavy  rains  so  that  its  condition  was  nearly  perfect.  With  the 

*  One  mile  uortheast,  as  estimated  by  Mr.  Wiessner. 

73 
10  E   S 


74  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

exception  of  a  few  patches  of  cirro-cumulus  about  10  a.  m.,  which  disappeared  soon 
after,  and  faint  traces  of  clouds  about  the  time  of  totality,  the  sky  remained  cloudless 
all  day. 

I  began  about  half  past  8  to  take  altitudes  of  the  sun,  and  continued  at  short 
intervals  for  two  hours. 

On  measuring  the  diameter  of  the  sun  after  the  observations  it  was  found  that  the 
horizon  glass  was  out  of  adjustment,  so  that  the  two  images  of  the  sun  could  be 
brought  to  cover  each  other  only  about  half  way,  but  it  was  thought  best  not  to  dis- 
turb the  adjustments  for  the  afternoon  series,  as  it  would  be  impossible  to  tell  what 
the  correction  would  be  to  the  forenoon  altitudes. 

In  the  afternoon  the  corresponding  altitudes  were  observed  for  all  but  two  or  three 
of  the  last  sets,  which  were  lost,  owing  to  a  mistake  in  the  time. 

The  resulting  correction  of  the  chronometer  at  apparent  noon  is  +  S1'  53™  I58-7O.* 

The  large  telescope  was  mounted  in  the  morning,  and  some  attempts  were  made 
to  place  it  in  such  a  position  as  to  enable  it  to  follow  the  sun  with  but  one  motion,  but 
it  was  not  got  very  near  in  the  meridian. 

The  instrument  being  provided  with  several  eye-pieces,  some  experiments  were 
made  to  determine  which  one  it  would  be  best  to  use,  and  I  decided  to  use  the  lowest 
power,  with  a  magnifying  power  of  34  diameters,  the  higher  powers  not  giving  a  view 
of  the  whole  disk  of  the  sun  and  the  definition  not  being  as  good  with  them.  The 
instrument  is  provided  with  a  diagonal  eye-piece,  having  a  thin  glass  plate  in  the  angle, 
to  let  most  of  the  light  pass  through  without  reflection;  several  caps  were  made  with 
apertures  of  different  sizes  to  shut  off  the  light,  but  with  the  smallest  aperture  about 
one  inch  in  diameter  it  was  found  necessary  to  have  a  colored  glass  shade  up  to  near 
the  time  of  the  totality. 

As  no  computation  had  been  made  of  the  time  of  beginning  of  the  eclipse  I  did 
not  attempt  to  observe  that,  and  the  eclipse  had  been  several  minutes  in  progress  at 
the  time  it  was  first  noticed. 

The  following  in  regard  to  the  phenomena  noted  during  the  progress  of  the  eclipse 
was  written  out  two  or  three  days  afterward. 

The  times  noted  are  all  chronometer  times,  Net/us  1311  being  the  chronometer 
used. 

The  first  phenomenon  noted  was  the  disappearance  of  the  large  spot,  as  follows: 
breaking  of  the  ring  of  the  penumbra  of  the  spot,  ioh  31"'  50";  final  disappearance  of 
the  umbra,  32™  i". 

Shortly  afterwards  there  appeared  to  be  a  very  slight  elongation  of  the  cusps  of 
the  sun. 

The  next  thing  noted  was  the  disappearance  of  a  group  of  three  small  spots  near 
the  center  of  the  sun,  forming  a  small  triangle,  thus,  v,  the  middle  spot  being  much 
the  smallest  of  the  three.  Disappearance  noted  as  follows:  first,  ioh49m288;  second, 
ioh  5 im  38;  third,  ioh  52'"  24". 

The  disappearance  of  the  spot  near  the  sun's  limb  was  noted  at  i  ih  7'"  5".  Before 
this  time  the  sun's  limb  had  begun  to  have  a  tremulous  motion,  and  there  was  an  ap- 

*  Altitudes  of  several  stars  gave  5«.07  less,  but  they  were  vitiated  by  the  inaladjiistmeut  of  the  sextant.— C. 


EEPOET  OF  MR.  E.  P.  AUSTIN.  75 

/ 

pearance  of  light  streaming1  from  the  extremity  of  the  cusps,  but  I   was  not  quite 
certain  whether  it  was  an  optical  illusion  or  not. 

About  this  time  I  removed  the  cap  which  was  over  the  object-glass,  reducing  the 
aperture  to  about  one  inch,  and  removed  the  colored  glass,  the  small  rim  of  light  being 
still  so  brilliant  as  to  dazzle  the  eye;  bright  red  flames  burst  out  before  the  total  obscura- 
tion along  a  space  of  10°  or  20°  of  the  moon's  limb. 

At  about  1 11'  9™  25s  a  gentleman  near  by,  who  was  on  the  lookout  for  the  shadow, 
called  out,  "Here  it  comes,"  and  a  few  seconds  after,  "Here  it  is."  The  red  flames 
were  so  bright  that  I  failed  to  recognize  the  instant  of  total  obscuration,  but  at 
1 1 h  qm  40"  (5h  2m  56"  local  mean  time*)  I  saw  the  flames  moving  along  the  limb  of  the 
moon  and  concluded  that  the  sun  had  been  gone  5s  or  6a. 

Expecting  a  duration  only  of  25"  or  3O3,  I  at  once  began  to  look  for  the  reappear- 
ance. The  red  flames  traveled  along  the  moon's  limb,  and  at  i  ih  iom  38".  5  (5h  3™  54" 
local  mean  timef)  the  light  of  the  sun  reappeared  in  the  midst  of  the  flames  in  two 
distinct  points  which  closed  up  in  about  half  a  second.  I  then  looked  at  the  sky  for 
the  first  time.  The  whole  outline  of  the  moon  was  surrounded  by  a  brilliant  halo,  out 
of  one  side  of  which  came  the  dazzling  light  of  the  slender  thread  of  the  sun  now 
exposed. 

By  keeping  the  direct  rays  of  the  sun  out  of  the  field,  the  dark  outline  of  the 
moon  was  distinctly  visible  projected  on  the  corona  at  nh  15™  30".  End  of  eclipse, 
i2h  7"'  io8  (6h  om  26"  local  mean  time). 

Chickens  went  to  roost  several  minutes  before  the  totality,  and  turkeys  came  in 
from  the  fields. 

During  the  totality  the  only  thing  to  which  my  attention  was  particularly  attracted 
besides  the  red  flames  already  mentioned  was  a  very  large  protuberance  almost  exactly 
on  the  west  side  of  the  sun. 

Mr.  Fiirst  noted  the  duration  of  totality  with  the  naked  eye  to  be  70".  Venus 
and  Mercury  were  seen  by  the  by-standers  during  the  totality,  and  Venus  for  some 
time  before  and  after. 

The  day  had  been  very  hot,  with  considerable  wind,  which  died  out  almost  com- 
pletely about  the  time  the  sun  was  half  eclipsed.  At  this  time  everything  had  a  som- 
ber appearance,  and  the  heat  of  the  sun  was  no  longer  oppressive,  while  near  the 
totality  there  was  a  slightly  chilly  feeling.  Near  the  time  of  totality  slight  traces  of 
clouds  appeared  in  the  west. 

Mr.  Covert  noted  the  following  phenomena  with  the  binocular  previously  referred 
to: 

Disappearance  of  the  large  spot,  iou  32m  3".  At  i  ih  8m  o"  a  candle  flame  no  longer 
casts  a  shadow  on  white  paper  about  3  inches  distant. 

Beginning  of  total  phase 1 11'     9™  53" 

End  of  total  phase 1 1      io     58 

I  may  add  to  the  above  that  about  20™  or  3Om  before  the  totality  a  number  of 
bright  specks  were  seen  both  by  Mr.  Covert  and  myself  to  pass  through  the  field  of 

*  Time  of  disappearance,  5b  2m  45'.4i.     Predicted  from  the  Am.  Ephemeris. 
tTime  of  reappearance,  5b  2m  4S".7o.    Predicted  from  the  Am.  Ephemeris. 


76  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

view.  At  the  time  I  thought  them  to  be  small  objects  in  the  air  near  by,  but  they 
were  undoubtedly  of  the  same  nature  as  objects  seen  by  other  observers  at  different 
points  and  thought  to  be  meteors. 

During  the  totality  the  moon  appeared  to  be  hanging  free  in  the  sky  in  front  of 
the  corona. 

The  arc  of  the  moon's  limb  along  which  the  red  flames  were  visible  is  very  much 
underestimated  in  the  previous  description.  I  think  it  could  not  have  been  less  than 
45°,  probably  greater. 

The  red  flames  moved  during  the  totality  along  the  limb  of  the  moon  from  the 
point  of  disappearance  to  that  of  reappearance. 

After  the  eclipse  the  weather  became  much  warmer,  although  the  sun  was  so  near 
the  horizon. 

In  the  evening,  signals*  were  exchanged  by  telegraph  with  Burlington,  Monroe, 
and  Kewanee. 

Respectfully,  yours, 

E.  P.  AUSTIN. 

Prof.  J.  H.  C.  COFFIN, 

Superintendent  Nautical  Almanac. 

% • • • — • — 

*  The  results  of  these  comparisons  are  given  on  page  13. — C. 


REPORT 


OT 


PROF.  JAMES  C.   WATSON. 


MOUNT 


77 


REPORT  OF  PROF.  JAMES  C.  WATSON. 


MOUNT  PLEASANT,  IOWA. 

ANN  ARBOR,  October,  1869. 

DEAR  SIR:  I  have  the  honor  to  report  that,  in  accordance  with  your  request,  I  pro- 
ceeded to  Mount  Pleasant,  Iowa,  to  take  part  in  the  observation  of  the  total  eclipse  of 
August  7.  I  was  accompanied  by  Assistant  Prof.  George  B.  Merriman,  of  the  Uni- 
versity of  Michigan,  and  by  Hon.  D.  Mclntyre,  treasurer  of  the  University  of  Michigan. 

We  were  joined  at  Burlington  by  Prof.  J.  M  Van  Vleck,  of  Middletown,  Conn., 
and  his  assistant,  Mr.  William  Johnston,  and  we  arrived  at  Mount  Pleasant  on  the 
evening  of  Wednesday,  August  4.  Our  arrival  had  already  been  preceded  by  that 
of  Prof.  E.  C.  Pickering,  of  Boston,  and  Professor  Henry  Morton,  of  Philadelphia, 
with  a  corps  of  skilled  photographers.  The  object  of  our  visit  becoming  known,  we 
were  waited  npon  by  Professor  Mansfield,  Mayor  Strawn,  and  .other  prominent  citizens 
of  the  place,  by  whom  hospitalities  were  extended  and  a  desire  expressed  to  aid  in  any 
way  possible  the  successful  completion  of  the  arrangements  preliminary  to  the  obser- 
vations to  be  made. 

After  visiting  several  points  in  the  suburbs  of  the  city,  we  selected  the  inclosed 
grounds  of  the  Henry  County  Agricultural  Society  as  the  proper  place  for  an  observ- 
ing station,  and  on  making  known  our  selection  to  the  authorities  we  were  informed  by 
Mayor  Strawn  that  the  city  government  would  provide  any  structures  that  it  might  be 
necessary  to  erect.  The  point  selected  was  on  the  south  side  of  the  building  used  as 
a  hall  of  fine  arts,  and  the  only  additional  requisites  were  a  screen  to  protect  the  tele- 
scope used  for  photography  from  the  wind  and  a  dark  room  for  the  preparation  and 
development  of  the  plates.  These  preparations  were  partially  completed  on  Thursday. 
During  the  whole  of  Friday  a  rain-storm  prevailed,  with  a  northeast  wind,  and  all  the 
indications  seemed  to  be  that  our  expedition  would  not  be  successful. 

Toward  night  on  Friday  the  barometer  gave  feeble  indications  of  a  favorable 
change  of  the  weather;  and  as  nothing  had  been  possible  so  far  in  the  way  of  accu- 
rately determining  either  our  geographical  position  or  our  local  time,  it  was  deemed 
advisable,  in  accordance  with  your  programme,  to  compare  our  chronometer  with  yours 
at  Burlington  by  means  of  the  electric  telegraph.  This  comparison  was  duly  effected 
on  this  and  the- following  evening  by  transmitting  signals  in  both  directions. 

On  Saturday  morning  the  clouds  broke  away  and  during  the  entire  day  the  sky 
was  beautifully  clear.  The  details  of  our  observations  I  shall  now  proceed  to  give, 
commencing  with  those  for  our  geographical  position  and  local  time. 

79 


80  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

I  took  with  me  from  Ann  Arbor  a  comet-seeker,  by  Fitz,  of  4  inches  aperture, 
the  finder  ofour  large  equatorial,  and  a  sidereal  chronometer,  Negus,  No.  578.  At 
Burlington  you  provided  me  with  an  additional  chronometer,  Ney-iis  No.  i  233,  regu- 
lated to  mean  solar  time,  an  aneroid  barometer,  No.  33509,  and  a  sextant  by  Pistor 
and  Martins.  If  the  weather  had  been  favorable  I  intended  to  make  observations  on 
Thursday  and  Friday  for  geographical  position,  but  not  succeeding  an  attempt  was 
made  on  Saturday.  I  soon  found  that  the  nature  of  the  soil  was  such  that  no  point 
could  be  found  within  the  space  available  where  the  work  upon  the  building  and 
screen  did  not  by  vibration  render  the  surface  of  the  mercury  of  the  artificial  horizon 
so  unsteady  that  no  definite  reflected  image  could  be  obtained.  After  repeated 
attempts  during  the  forenoon  I  was  obliged  to  abandon  all  hope  of  getting  more  than 
an  approximation. 

At  noon,  when  nearly  all  the  workmen  were  absent,  I  succeeded  in  getting  the 
following  altitudes  for  latitude  : 

Chrou.  time.  Negus  1233.  ©'s  upper  limli. 

6h     om     8s  65°  35'  43" 

1  13  65  35  45 

2  21  65  36  15 
36  65  36  15 

4  12  65       36      20 

5  21  65       36      15 
7.1  65      36     20 

8  i7  65       35      45 

9  30  65       35      10 

The  corrections  of  the  sextant  have  already  been  applied  to  these  results. 

The  chronometer  time  of  apparent  noon  was  6h  4™  25",  and  hence  we  obtained  as 
the  resulting  latitude  +40°  56'  $9". 9. 

Just  before  the  commencement  of  the  eclipse  I  endeavored  to  get  a  determination 
of  local  time,  to  which  we  had  thus  far  only  a  rude  approximation. 

The  observations  were  as  follows: 

Chron.  time.  Negus  1233.  ©'»  upper  limit. 

9"  7'"  51"  43°  46'  55" 

8  46  43     37    15 

9  36  43     27    50 

10  32  43      18    15 

11  40  43       5     i5 


Means 99       41-0          43  27  6  .o 

Refraction —  1  o  .8 

Parallax .    +  6.5 

Semi-diameter —  15  49  -° 


True  altitude  0's  center.  .          43       10    22   .7 
Sun's  declination +  16°  15'  /'.8 


REPORT  OP  PROF.  JAMES  0.  WATSON.  81 

The  unsteadiness  of  the  mercury  occasioned  by  the  vibrations  produced  by  the 
motion  of  carriages  in  the  vicinity  was  such  that  the  measurements  were  made  with 
extreme  difficulty.  The  results  from  these  measurements  are  as  follows : 

Hour  angle 3h     5'"   i6".8 

Mean  time  of  apparent  noon o      5     27  .3 


Local  mean  time 3     10     44.1 

Chroniometer,  Negus  1 233 9      9     41  .o 


Chromometer  correction  on  local  time . . . .    +     6       [        3.1 

The  foregoing  are  the  best  observations  for  latitude  and  time  which  were  possible 
during  our  stay  at  Mount  Pleasant,  and  hence  I  suggested  to  you  the  propriety  of 
sending  some  person  there  to  make  a  better  determination  of  latitude  and  to  determine 
also  the  difference  of  longitude  between  Mount  Pleasant  and  Burlington  in  order  that 
the  telegraphic  comparison  of  chronometers,  might  be  available  for  accurate  local  time, 
the  observations  at  Burlington  having  been  made  with  a  transit  instrument.  This 
service  was  performed  by  Mr.  Wiessner.* 

In  obtaining  the  correction  of  the  chronometer  for  the  reductions  of  the  times  of  the 
phenomena  observed  it  is  of  course  proper  to  adopt  only  the  results  of  the  comparisons 
of  chronometers,  in  connection  with  Mr.  Wiessner's  longitude  determination.f 

Further  comparisons  were  made,  using  at  Mount  Pleasant  chronometer  Negus  578, 
it  having  been  our  intention  to  use  both  chronometers  during  the  observations  of  the 
eclipse,  one  for  astronomical  observations  and  the  other  for  the  records  of  the  pho- 
tographers. It  was  found  advisable  at  the  time  of  the  observations  to  use  but  one 
chronometer,  and  the  mean-time  chronometer,  Negus  1233,  was  so  used. 

I  have,  therefore,  adopted  the  following  correction:  August  7,  4h  Mount  Pleasant 
mean  time,  Negus  1233,  -f  6h  im  28.26,  with  a  daily  variation  of  -f  os.22,  with  which 
the  observed  times  of  contacts  have  been  reduced. 

Our  arrangements  for  observations  were  completed  only  half  an  hour  before  the 
first  contact  was  observed.  In  addition  to  the  telescopes  already  mentioned,  Professor 
Van  Vleck  had  brought  out  a  very  fine  portable  equatorial,  by  Clark,  with  which  his 
spectroscopic  observations  were  made,  and  also  the  finder  of  the  Middletown  equatorial, 
also  by  Clark,  and  an  equatorial  stand.  It  was  with  the  latter  telescope,  aperture  y/* 
inches,  and  magnifying  power  of  about  80  diameters,  that  my  own  observations  were 
made.  Professor  Morton  had  the  Philadelphia  telescope  for  photographic  purposes. 
Since  these  gentlemen  will  make  detailed  reports  of  their  operations,  no  further  account 
of  their  observations  is  here  necessary.  Professor  Merriman  observed  with  the  Ann 
Arbor  comet-seeker,  magnifying  power  25,  and  Mr.  Mclntyre  observed  as  an  amateur 
with  the  finder  of  the  Ann  Arbor  equatorial,  magnifying  power  30. 

*|His  results  are  given  in  his  report,  page  70. — C. 

tThe  results  of  these  comparisons  are  included  in  the  tables,  pages  15  and  16. — C. 

11  ES 


82  ECLIPSE  OP  THE  SON,  AUGUST  7,  lS(i!». 

The  phases  of  the  eclipse  were  observed  as  follows,  the  chronometer  being  Neyus 

1233: 

I'"trst  contact. 

Observer.  Cliron.  time. 

Watson.  .    9"  53'"     3«.s 

Merriman 9     53       4  .o 

Van  Vleck 9    53       o 

Beginning  of  total  eclipse. 

Watson 10  54  27.5 

Merriman i o  54  29  .o 

Mclntyre 10  54  27.0 

End  of  total  eclipse. 

Watson 10  57  19.5 

Merriman 10  57  200 

Mclntyre i  o  57  20.0 

Last  contact. 

Watson.  ii  53  34.5 

Merriman 1 1  ^3  32  .5 

Van  Vleck 11  53  30.5 

Professor  Van  Vleck  was  occupied  with  spectroscopic  observations  during  the 
total  phase,  and  hence  he  did  not  observe  the  times  of  beginning  and  end  of  that 
phase.  Mr.  Mclntyre  did  not  catch  the  first  contact  of  limbs. 

Applying  the  correction  already  determined  as  above  for  the  chronometer,  we 
obtain  the  following  results: 

First  contact. 

Observer.  Mount  Pleasant  mean  time. 

Watson 3h  54™     5*.  76 

Merriman 3     54       6  .26 

Van  Vleck  ...  3     54       2 .3 

[Predicted  from  American  Epheineris.] 3     53  41.20 

Beginning  of  total  eclipse. 

Watson.  4  55  29.75 

Merriman 4  55  31.25 

Mclntyre  .  ...  4  55  29 .25 

[Predicted  from  American  Ephemcris.] 4  55  20  . 10 

End  of  total  eclipse. 

Watson. 4  58  21.75 

Merriman 4  58  22.25 

Mclntyre 4  58  22  .25 

[Predicted  from  American  Ephemeris.] 4  58       9  .o 


REPOKT  OF  PKOF.  JAMES  C.  WATSON.  83 

'  Last  contact. 

Mount  Pleasant  moan  time. 

Watson.  ..5  54  36.74 

Merriman  .  .    5  54  34.74 

Van  Vleck 5  54  32.8 

[Predicted  from  American  Ephemeris.] 5  54  22  .07 

The  times  of  beginning1  and  end  of  the  total  phase  were  observed  by  me  without 
the  interposition  of  a  shade-glass.  By  the  other  observers  the  shade-glasses  were 
used. 

During  the  progress  of  the  eclipse  I  noticed  particularly  the  form  and  extent  of 
the  solar  cusps,  and  the  same  was  done  by  the  other  observers.  These  cusps  were 
observed  by  us  to  be  remarkably  distinct  and  attenuated  at  the  extremities  during  the 
entire  period  of  their  visibility.  Mr.  Mclntyre  and  myself  both  noticed  a  flash  of 
light  from  the  upper  cusp  as  seen  in  the  telescope  about  five  minutes  before  the 
beginning  of  total  obscuration,  but  careful  scrutiny  failed  to  reveal  any  repetition  of 
the  phenomenon  either  before  or  after  the  total  obscuration. 

The  formation  of  Baily's  beads  was  very  distinct  a  few  seconds  before  the 
beginning  of  total  obscuration  and  immediately  after  the  end  of  the  total  phase. 
Those  which  preceded  were,  however,  very  different. 

[NoTE. — Professor  Watson's  drawings  of  these  appearances  are  given  in  figures 
3  and  4,  Plate  I]. — C. 

A  very  large  protuberance  was  visible  on  the  lower  limb  of  the  sun  of  a  beautiful 
rose  color,  and  so  brilliant  that  to  the  naked  eye  it  appeared  to  indent  the  moon's  limb. 
[See  Fig.  2,  Plate  I.]  As  seen  in  the  telescope  immediately  after  the  beginning  of  the 
total  obscuration  a  chaiu  of  rose-colored  prominences  took  the  place  of  Baily's  beads. 
I  wa,s  careful  to  notice  the  interval  of  the  moon's  passage  over  these  protuberances, 
and  I  found  that  the  principal  chain  was  occulted  in  20  seconds,  while  two  higher 
prominences  near  the  point  of  internal  contact  were  visible  10  seconds  longer.  At  ioh 
56™  2 5s.o,  chronometer  time,  a  prominence  became  visible  on  the  opposite  limb  of  the 
sun,  and  at  i£>h  57™  6".o  still  another  became  visible  about  midway  between  this  and  the 
one  visible  to -the  naked  eye. 

At  the  middle  of  the  eclipse  I  glanced  for  a  moment  at  the  appearance  of  the  sky 
and  of  surrounding  objects.  Stars  of  the  third  magnitude  were  distinctly  visible. 
The  northeastern  and  southwestern  portions  of  the  sky  in  the-  vicinity  of  the  horizon 
were  illuminated  strongly  by  the  light  beyond  the  limits  of  the  shadow.  The  western 
sky  exhibited  a  greenish  tint.  Persons  standing  near  whom  I  had  requested  to  notice 
particularly  the  approach  of  the  shadow  reported  that  they  could  not  detect  any  change 
in  the  appearance  of  distant  objects  as  it  approached,  but  that  the  sky  exhibited  it  most 
clearly.  The  gradual  diminution  of  the  sunlight,  as  the  eclipse  progressed,  had  unfitted 
those  who  had  been  watching  throughout  for  noticing  contrasts  of  light,  which  would 
otherwise  have  been  so  remarkable.  The  sudden  appearance  of  the  corona  was  greeted 
with  shouts  of  applause,  heard  from  all  parts  of  the  city,  and  we  noticed  that  cattle 
grazing  in  the  vicinity  gave  unmistakable  signs  of  astonishment.  The  light  during 
the  total  obscuration  was  estimated  as  about  equal  to  that  of  a  moonlight  night  when 


84  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

the  moon  is  ten  days  old,  with  this  difference,  however,  that  there  were  no  distinct 
shadows.  The  secondary  tints  of  shade  which  give  relief  and  reality  to  the  image 
were  wanting,  and  as  a  consequence  persons  standing  near  had  a  peculiar  ghost-like 
appearance.  The  subsequent  change  from  darkness  to  the  full  glare  of  day  did  not 
appear  so  remarkable  as  the  contrary  had  been.  The  first  returning  rays  of  the  sun 
darted  forth  instantaneously  with  extraordinary  brilliancy,  and  the  profound  silence 
which  had  reigned  gave  way  to  an  audible  hum.  The  world  seemed  to  breathe  again, 
and  at  once  life  and  animation  took  the  place  of  what  was  an  oppressive  stillness. 

In  closing  this  report  I  must  not  fail  to  acknowledge  our  obligations  for  intelligent 
assistance  rendered  by  Professor  and  Mrs.  Mansfield,  of  Mount  Pleasant,  and  also  by 
Mr.  B.  C.  Alexander  arid  Mr.  Frank  Krause,  graduates  of  the  engineering  department 
of  the  University  of  Michigan.  Mrs.  Mansfield  made  the  record  for  Professor  Van 
Vleck's  spectroscopic  observations.  Mr.  Alexander  called  the  seconds  from  the  dial 
of  the  chronometer,  and  Mr.  Krause  recorded  the  instants  of  the  exposure  of  the 
photographic  plates.  Professor  Mansfield  noted  the  readings  of  the  aneroid  barometer 
as  follows: 

In. 

30  minutes  before  total  obscuration 29.590 

1 5  minutes  before  total  obscuration 29-595 

At  beginning  of  total  phase 29.580 

4  minutes  after  total  obscuration 29-572 

10  minutes  after  tetal  obscuration  . . 29.570 

1 5  minutes  after  total  obscuration 29-567 

20  minutes  after  total  obscuration 29.565 

25  minutes  after  total  obscuration 29.562 

At  the  last  contact 29.561 

The  reduction  to  be  applied  to  these  readings  is  —  oin.8oo,  as  determined  August  8 
at  Burlington.     Meteorological  observations  during  the  eclipse  were  made  by  Professor 
Pickering  at  the  hotel  in  the  city,  and  hence  no  others  were  made  by  us  at  our  station. 
Our  grateful  acknowledgments  are  due  to  many  citizens  of  Mount  Pleasant  for 
courtesies  extended,  and  especially  to  Colonel  Root,  proprietor  of  the  omnibus  line, 
who  furnished  carriages  at  all  times,  free  of  expense,  to  convey  members  of  our  party 
to  and  from  the  observing  station. 
Very  truly,  yours, 

JAMES  C.  WATSON. 
Prof.  J.  H.  C.  COFFIN, 

Superintendent  Nautical  Almanac. 


REPORT 


PROF.   J.   M.  VAN  VLECK 


MOTJ^TT 


REPORT  OF  PROF.  J.  M.  VAN  VLECK. 


MIDDLETOWN,  October  15,  1869. 

DEAR  SIR:  I  respectfully  submit  the  following  report  of  my  observations  of  the 
solar  eclipse  of  August  7: 

My  station  was  Mount  Pleasant,  Iowa,  at  which  place  I  arrived  in  company  with 
Professor  Watson  and  others  on  the  evening  of  the  4th. 

The  special  duty  assigned  to  me  was  that  of  spectroscopic  observation.  I  under- 
took also  to  observe  the  first  and  last  contacts. 

The  instruments  which  I  employed  were  made  under  your  direction  by  Messrs. 
Alvan  Clark  &  Sons,  and  were  used  for  the  first  time  on  the  day  of  the  eclipse. 

The  spectroscope  has  a  single  prism  of  glass  with  a  refracting  angle  of  60°.  It 
is  accompanied  by  a  scale  of  equal  parts,  which  is  illuminated  by  a  hand-lamp,  and 
read  by  reflection  from  the  surface  of  the  prism. 

The  telescope  has  an  aperture  of  3^  inches,  and  a  focal  length  of  38  inches.  It 
is  supported  by  a  tripod,  with  an  equatorial  mounting  adjustable  to  latitude,  but  with- 
out slow-motion  screws. 

In  observing  the  beginning  and  end  of  the  eclipse  I  used  a  direct-vision  eye- 
piece, with  the  full  aperture  of  the  telescope.  The  magnifying  power  was  34.  The 
screen  -glass  was  of  a  deep  green  color.  I  received  it  from  Professor  Watson  in  ex- 
change for  the  screens  of  neutral  tint  which  accompanied  my  telescope. 

I  watched  carefully  for  any  indication  of  the  approach  of  the  moon's  limb  before 
the  first  contact,  but  could  discover  none.  Neither  did  I  see  any  traces  of  it  after  the 
final  contact. 

The  times  at  which  I  saw  the  contacts  were,  by  the  chronometer  (Negus  1233), 
as  follows: 

Time  of  first  contact 9h  53™  os 

Time  of  last  contact 1 1     53    30.5 

For  the  guidance  of  the  telescope  during  the  spectroscopic  observations,  I  was 
indebted  to  my  friend,  Mr.  W.  A.  Johnston,  of  this  city.  In  the  absence  of  slow- 
motion  screws  this  was  a  task  of  much  delicacy,  and  it  was  skillfully  performed. 

Our  telescope  had  a  small  finder,  which,  though  adequate  to  the  usual  demands 
upon  it,  was  probably  not  made  with  reference  to  the  requirements  of  the  spectro- 
scope. A  slight  examination  of  it  convinced  us  that  it  would  be  safer  to  depend  upon 
the  image  of  the  sun  or  corona  at  the  slit  of  the  spectroscope.  The  diameter  of  this 
image  was  about  an  inch  and  a  quarter.  It  was  obtained  from  the  smaller  image  at 

87 


88  ECLIPSE  "OF  THE  SUN,  AUGUST  7,  1869. 

the  focus  of  the  telescope  by  inserting  a  negative  eye-piece  at  the  proper  place  in  the 
tube  which  connected  the  two  instruments.  As  a  finder  it  gave  all  the  precision  that 
was  needed.  The  principal  objection  to  it  was  its  faintness  at  the  time  of  totality. 
It  was  with  difficulty  that  any  of  the  protuberances  could  be  distinguished  upon  it, 
and  we  were  obliged  to  depend  mainly  on  the  spectroscope  to  determine  their  position. 

Anticipating  that  this  would  be  the  case,  it  was  my  intention  to  examine  the  sun's 
border  before  the  eclipse,  in  order  to  ascertain  the  position  of  the  largest  prominences. 
But  the  unfavorable  weather  of  the  two  preceding  days  had  delayed  the  work  of  our 
party  so  much  that  our  time  on  the  7th  had  to  be  devoted  to  other  preparations. 

At  the  beginning  of  the  totality,  we  had  the  slit  of  the  spectroscope  in  contact 
with  the  moon's  limb,  about  30°  south  of  the  east  point.  A  spectrum  of  bright  lines, 
which  appeared  as  soon  as  the  light  of  the  sun  vanished,  indicated  that  we  were  upon 
a  protuberance.*  I  attempted  at  once  to  determine  the  positions  of  these  lines,  but  the 
difficulty  of  holding  our  instruments  in  position  was  such  that  we  found  it  necessary 
to  seek  a  larger  protuberance.  For  this  purpose  the  telescope  was  moved,  without 
changing  the  direction  of  the  slit,  towards  the  east  point.  Not  far  from  this  point  we 
found  a  prominence  of  such  size  that  it  could  be  distinguished  by  Mr.  Johnston  in  the 
image  of  the  corona.  It  was  probably  the  large  protuberance f  described  by  Professor 
Morton  as  resembling  in  shape  the  letter  X.  The  spectrum  in  this  place  appeared  to 
me  to  be  identical  with  the  former  one.  The  unsteadiness  of  the  instrument  still  inter- 
fered somewhat  with  the  precision  of  my  measurements  ;  but  I  think  that  there  can  be 
no  difficulty  in  identifying  my  results  with  the  more  accurate  determinations  of  other 
observers.  The  following  are  my  readings  for  the  bright  lines  compared  with  the 
positions  of  a  few  of  the  principal  dark  lines  of  the  solar  spectrum.  The  latter  were 
measured  before  the  eclipse. 

Bright  lir 

1  43.5 

2  51.5 
"?  6l.5 

tJ  *J 

4  72 

5  85 

6  91 

7  103? 

The  readings  for  the  first  and  last  of  the  bright  lines  were  not  precise.  They  are, 
however,  well-known  lines  whose  positions  had  been  previously  determined  with  great 
accuracy.  The  first,  fourth,  sixth,  and  seventh  are  hydrogen  lines  whose  places  on 
Kirchhoff's  scale  are  C,  F,  2796  and  h,  respectively.  The  second  is  the  well-known 
line  D3  of  the  chromosphere,  situated  just  above  I).  Its  place  on  the  same  scale  is 
1017  5.  The  third  is  a  little  below  E,  and  is,  I  presume,  Kirchhoff's  1474  which  cor- 
responds to  an  iron  line,  and  had  been  previously  discovered  as  a  chromosphere  line 
"by  Mr.  Lockyer,  also  at  a  later  date  by  Professor  Young.  So  far  as  I  can  judge  from 
a  graphic  comparison  of  the  two  scales,  the  fifth  line  corresponds  nearly  with  Kirch- 
hofPs  2600. 

*  Probably  No.  5  of  Mayer's  diagram,  Plato  X,  Fig.  I.— C. 
tNos.  3  and  4  of  Mayer's  diagram.— C. 


»es. 

c 

Dark  lines. 
A-l 

D 

to 

C  T 

j  • 

61  9 

F 

72 

G 

.h 

IO2 

REPORT  OF  PROF.  J.  M.  VAN  VLECK.  89 

While  the  measurements  were  in  progress,  the  instrument  was  held,  of  necessity, 
with  as  much  steadiness  as  possible  directly  upon  the  protuberance.  At  first  it  seemed 
to  be  oscillating  between  the  lower  part  of  this  object  and  the  dark  surface  of  the  moon 
At  this  time  all  of  the  lines  were  visible  in  quick  flashes,  alternating  with  darkness ; 
but  I  perceived  no  light  from  the  corona.  Presently,  however,  a  slight  movement 
brought  us  upon  the  corona,  which  gave  a  continuous  spectrum,  with  none  of  the  dark 
lines  of  the  solar  spectrum.  There  was  also,  at  the  same  time,  a  noticeable  change  in 
the  appearance  of  the  bright  lines.  In  the  former  position  I  had  observed  little  or  no 
difference  in  their  lengths.  But  now,  the  second  and  third  lines  of  the  above  list,  or 
those  near  D  and  E,  respectively,  extended  entirely  across  the  spectrum,  though  none 
of  the  others  had  half  as  great  a  length.  Once,  also,  when  a  small  displacement  of  the 
telescope  put  the  others  just  out  of  the  field,  these  two  lines  continued  in  view  with 
the  same  length,  in  connection  with  the  corona-spectrum.  This  appearance  lasted 
only  for  an  instant,  and  was  not  repeated.  Whether  the  two  lines  had  equal  lengths, 
or  to  what  distance  they  extended,  I  cannot  tell.  My  efforts  were  directed,  at  the 
time,  to  the  identification  of  the  lines  above  E,  and  I  failed  to  give  the  phenom- 
enon the  attention  it  deserved.  But  so  far  as  I  have  described  it,  1  am  confident  of  my 
correctness. 

A  short  time  before  the  reappearance  of  the  sun,  we  moved  to  some  distance  from 
the  protuberance.     But  I  saw  nothing  besides  the  continuous  spectrum  of  the  corona. 
Most  respectfully,  your  obedient  servant, 

J.  M.  VAN  VLECK. 

Prof.  J.  H.  C.  COFFIN, 

Superintendent  of  the  Nautical  Almanac,  Washington,  D.  C. 

12  E  8 


REPORT 


OF 


PROF.  E.  C.  PICKERING. 


MOUNT  PLEASANT,  IOWA.. 


91 


REPORT*  OP  PROFESSOR  EDWARD  C.  PICKERING. 

MOUNT  PLEASANT,  IOWA. 

[Professor  Pickering  was  a  member  of  the  "Philadelphia  Photographic  Expedi- 
tion." His  report  is  inserted  here  from  its  close  connection  with  that  of  Professor  Van 
Vleck.— J.  H.  C.  COFFIN.] 


MOUNT  PLEASANT,  IOWA,  August  9,  1869. 
Prof.  HENRY  MORTON: 

DEAR  SIR  :  The  following  experiments  were  conducted  at  the  Brazelton  House  in 
this  town.  Latitude,  40°  57'  north;  longitude,  91°  38'  west.  The  room  used  was  in 
the  third  story,  and  had  an  unobstructed  view  to  the  west. 

TABLE  I. 


Time. 

A. 

B. 

C. 

Time. 

A. 

B. 

C. 

h.     m. 

O 

0 

o 

h.     m. 

o 

O 

O 

3       7 

23-3 

23-1 

40.8 

5     10 

23.0 

23.1 

26.4 

20 

23-5 

23.0 

40.8 

«5 

23.2 

27.6 

29 

23-7 

23.2 

40.8 

20 

23-4 

23-4 

28.7 

36 

23.8 

23.  2 

41-7 

25 

23.  6 

23.6 

29.  6 

40 

23-9 

23-4 

41.7 

30 

23-8 

31.0 

5° 

24-3 

24.0 

.  42.2 

35 

24.0 

24.  o 

32.0 

55 

24.7 

24.  o 

42.0 

40 

24.3 

24.0 

32-4 

4      o 

24.7 

24.0 

41.8 

45 

24.4 

24.2 

33-  i 

5 

24.9 

24.0 

40.8 

50 

24.5 

24.2 

32.90 

10 

24.9 

24.  o 

40.  6 

55 

24.7 

24-3 

35-4 

'5 

25.0 

24.  o 

39-7 

6      o 

24.  6 

36.9 

20 

25-3 

24.0 

38-0 

5 

24-5 

24.2 

35-8 

25 

25.2 

24.  1 

37-4 

18 

24.2 

34-8 

30 

24.7 

24.  o 

34-9 

20 

24-3 

24.0 

34.1 

35 

24.4 

33-o 

25 

24.2 

24.0 

33-9 

40 

24-3 

.... 

31-8 

3° 

23-9 

32-9 

45 

23-9 

23.8 

28.6 

35 

23-8 

30.7 

48 

23-7 

27.2 

40 

23-5 

23-7 

29.7 

57 

23-3 

23-3 

24.8 

45 

23.2 

27.1 

5r\ 

?1    A 

2d    7 

CQ 

2<,.  2b 

u 

?3*  4 

^^r-  / 

J" 

j 

5 

23 

25-3 

55 

22.7 

23.0 

23-4<- 

a,  shadow  fell  on  C,  causing  the  depression  seen  in  the  curve. 

b,  sun  reaches  cloud  near  horizon. 

c,  sun  appears  red  through,  cloud. 


•Reprinted  from  Journal  of  the  Franklin  Institute,  vol.  LVIII,  third  series,  p.  SJ»1. 


93 


94 


ECLIPSE  OF  THE  SUN~,  AUGUST  7,  1869. 


The  most  important  experiments  during  the  partial  phase  were  thermometric. 
For  this  purpose  three  delicate  thermometers  were  used.  An  alcohol  thermometer,  A, 
divided  to  half  degrees,  and  two  filled  with  mercury,  B  and  C,  the  latter  having  a 
blackened  bulb.  A  was  hung  in  the  room  in  the  shade ;  B  kept  in  its  case,  so  that  its 
temperature  was  very  nearly  constant;  and  C'was  exposed  dii'ectly  to  the  sun's  rays. 

Observations  were  made  every  5  minutes  after  the  eclipse  began;  at  longer  intervals 
before.  The  time  is  about  a  minute  and  a  half  slower  than  the  local  time,  or  56™  50" 
slower  than  Washington  mean  time.  The  temperatures  are  centigrade,  estimated  to 
tenths  of  a  degree. 

The  curves  in  the  adjoining  figure  represent  these  results;  vertical  distances  give 
temperatures ;  horizontal  distances,  times.  For  use  in  the  following  table,  they  have 


FIG.  1. 


also  been  drawn  on  a  much  larger  scale,  and  the  accidental  errors  in  part  eliminated 
by  passing  a  curve  through  all  the  points ;  the  difference  was  generally  only  a  small 
fraction  of  a  degree.  The  times  were  then  computed  at  which  i,  2,  3,  4,  &c.,  digits 
were  eclipsed,  and  the  corresponding  temperatures  obtained  by  interpolation. 

In  Table  II  the  first  column  gives  the  number  of  digits  eclipsed;  negative 
numbers  denoting  distances  between  the  two  limbs.  The  second  column  gives  the 
local  time ;  the  third,  the  temperature  of  A  ;  the  fourth,  the  estimated  temperature,  if 
there  had  been  no  eclipse.  Of  course  this  is  a  very  rough  approximation,  and  was  ob- 
tained by  drawing  a  continuous  curve  through  the  beginning  and  end  of  the  eclipse. 
It  is  only  intended  as  a  guide,  and  too  much  dependence  must  not  be  put  upon  it. 
The  last  column  gives  the  fraction  of  the  sun's  disk  obscured. 

By  examining  the  third  column  of  this  table,  it  will  be  seen  that  shortly  before 
the  eclipse  the  thermometer  rose,  attaining  its  maximum  at  the  instant  of  contact, 
so  that  when  three  digits,  or  25  per  cent,  of  the  sun's  disk  was  obscured,  the  tempera- 
ture was  about  the  same  as  before  the  eclipse.  Again,  the  thermometer  continued  to 
rise  after  the  eclipse  was  over. 


REPORT  OF  PROF.  E.  C.  PICKERING. 
TABLE  II. 


Digits. 

Time. 

Temperature. 

Obscur. 

Digits. 

Time. 

Temperature. 

Obscur. 

Real. 

Assumed. 

Real. 

Assumed. 

—  8 

-  7 
—  6 

—  5 
-  4 
—  3 

2 
I 
0 

I 
2 

3 
4 
S 
6 

7 
8 

9 

10 

ii 

12 

li.      m. 
3       8 
13 
19 
25 
3° 
36 
42 
47 
53 
58 
4       4 
9 
'5 
20 

25 
3" 
36 
4i 
46 

5' 
56 

o 

40.8 

40.8 
40.8 
40.8 
40.9 
41.5 
41.8 
42.0 

42.  1 

42.  o 

41-3 
40.7 

39-6 
38.6 

37-4 
34-9 
33-° 
3'-7 
28.6 
26.4 
24.8 

o 

12 

II 

IO 

9 

8 

7 
6 

5 
4 
3 

2 

I 
0 

—    2 

-  3 
-  4 

£ 

—  6 

-  7 
—  8 

1).     m. 
4     59 
5       4 
9 
M 
'9 
24 
28 

32 

37 
41 
45 
5o 
5« 
58 

6         2 

7 
ii 

'5 
'9 
23 
26 

O 

24.7 
25.1 
25.9 
27.1 
28.2 
29-3 
3°-  i 
3i-3 
32-' 
32-8 
33-5 
34-4 
35-2 
36.1 
36.1 
35-7 
35-3 
35-o 
34-4 
33-9 
33-5 

o 

39.5 

39-3 
39-  i 
38.9 
38.7 
38.5 
38.3 
38-0 
37-8 
37-6 
37-3 
36.9 
36.6 

36.3 

I.OOO 

•893 
•789 
.685 
.586 
.486 

•39" 
.302 
.219 

•  '44 
.079 
.029 
.000 

40.8 
40.8 
40.8 
40.7 
40.7 
40.7 
40.  6 
40.  6 
40.5 
40.4 

40.3 
40.  2 
40.  I 
40.0 

39-9 
39-8 
39-6 

.029 
.  029 
•  144 
.  219 

.302 

•391 
.486 

.586 
.685 
.789 
•893 

I.  000 

Columns  A  and  B,  in  the  first  table,  show  that  the  temperature  of  the  air  falls 
but  slightly.  As  the  instruments  were  in  the  room,  they  were  protected  from  radiation. 
Their  maxima  occurred  some  time  after  the  first  contact,  owing^to  the  gradual  warming 
of  the  room  by  the  sun.  In  the  last  column  of  the  second  table,  the  disks  of  the  sun 
and  moon  are  supposed  to  be  of  the  same  size;  as  the  latter,  in  reality,  exceeded  the 
former  by  about  one  twenty-fifth,  the  area  obscured  would  be  somewhat  greater.  The 
error,  however,  is  only  about  one  per  cent,  for  eleven  digits,  aiid  much  less  for  other 
parts  of  the  eclipse. 

Actinometric  experiments  by  the  method  of  Bunsen  and  Roscoe  were  made, 
exposing  pieces  of  sensitive  paper  every  five  minutes  for  one 
minute  to  the  sun,  and  then  comparing  them  with  a  fixed  scale. 
The'results  are  given  in  Table  III  and  in  Fig.  2,  but  the  delicacy 
of  the  method  does  not  appear  to  lead  to  important  results. 


Fig.  2. 


96 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1809. 
TABLE  III. 


Time.      Intensity. 

Time.      Intensity. 

Time.      Intensity. 

h.    m. 

h.    in. 

h.    in  . 

3     40         85 

4     35         20 

5     10        25 

4       5         60 

4     40         15 

5     20        25 

4     20         50 

4    45           8 

5     35        36 

4     25         45 

4     5°           i 

5     40        3° 

4     3°        3° 

5      5          8 

5     59        25 

THE    TOTAL    PHASE. 

On  the  approach  of  totality  the  thermometric  and  acti  no  metric  experiments  were 
given  up,  and  the  following  observations  made  instead: 

GKNKRAL,  OBSERVATIONS. — A  pocket  telescope  magnifying  about  ten  diameters  was 
used.  It  was  tied  to  the  baqk  of  a  chair  by  a  piece  of  cloth  just  tightly  enough  to 
make  it  remain  in  whatever  position  it  was  placed.  This  forms  a  convenient  mounting, 
and  by  it  the  telescope  can  be  moved  steadily,  and  the  sun  or  a  star  followed  without 
difficulty. 

The  corona  appeared  as  an  irregular  four-pointed  star,  with,  of  course,  a  black 
center.  Two  of  the  rays  were  nearly  vertical,  and  two  horizontal,  the  left  hand  one 
pointing  somewhat  downward,  while  between  it  and  the  lower  ray  was  a  fifth  smaller 
point.  Its  color  was  pure  white,  very  different  from  the  full  moon,  but  resembling  a 
cumulus  cloud.  Possibly  the  reddish  tint  noticed  by  many  observers  heretofore  may 
be  a  subjective  effect  due  to  the  green  color  of  surrounding  trees  or  grass.  Its  texture 
resembled  the  ragged  edge  of  a  thunder  cloud,  or  the  crest  of  a  wave  torn  by  the  wind. 
The  striae  were  not  radial  but  spiral,  as  if  the  sun  had  been  turned  in  such  a  way  that 
the  upper  edge  moved  towards  the  east. 

A  very  bright  protuberance  was  seen  on  the  lower  edge  of  the  sun ;  also,  two 
others  on  the  western  side.  The  first,  to  the  naked  eye,  appeared  as  much  within  as 
without  the  moon's  limb,  and,  by  irradiation,  appeared  to  send  rays  some  distance 
towards  the  center.  The  sky  presented  the  appearance  it  has  during  the  morning 
twilight,  the  western  horizon,  however,  being  bright  yellow. 

I  did  not  notice  the  sudden  lowering  of  the  temperature  during  totality,  although 
this  was  very  perceptible  to  those  in  the  open  air;  it  would,  therefore,  seem  that  this 
is  an  effect  mainly  due  to  radiation. 

After  the  reappearance  of  the  sun  the  corona  remained  visible  for  several  seconds. 
Cocks  in  the  neighborhood  crowed  repeatedly  as  the  light  returned. 

The  following  star  observations  were  made  by  Dr.  C.  Pearson,  who  also  assisted 
in  the  actinometric  observations.  Mercury  became  visible  at  4b  54™,  or  two  minutes 
before  totality,  and  disappeared  at  5b.  Venus  was  visible  from  4h  51™  to  5h  12™,  or 
twenty-one  minutes. 

SPKCTROSCOPIC  OBSERVATIONS. — A  chemical  spectroscope  with  one  60°  prism  was 
loaned  me  by  Professor  Van  Vleck,  and  was  mounted  in  the  way  above  described  for 
the  telescope.  As  no  lens  was  placed  in  front  of  it,  all  the  light  that  fell  on  the  slit 
from  a  circle  about  7°  in  diameter  passed  through  the  instrument.  Turning  it  towards 


EEPOET  OF  PEOF.  E.  C.  PICKEEING.  97 

the  sun  before  totality,  the  latter  remained  in  the  field.  This  is  probably  the  best 
way  to  obtain  the  spectrum  of  the  corona,  as  there  is  very  little  loss  of  light.  The 
protuberances  are  so  small  that  their  spectra  would  be  faint.  The  spectrum  appeared 
to  be  continuous,  with  two  or  three  bright  lines,  the  brightest  in  the. neighborhood  of 
E,  and  the  next  near  C;  but  as  no  dark  solar  lines  were  visible,  these  positions  cannot 
be  relied  upon.  The  absence  of  the  dark  lines  may  be  due  to  the  want  of  brilliancy 
of  the  spectrum,  although  this  was  bright  enought  to  have  its  upper  and  lower  edges 
well  defined. 

POLARIZATION. — The  form  of  polariscope  used  was  that  adopted  by  Arago  in  his 
experiments  on  sky  polarization.  It  consists  of  a  tube  about  20  inches  long  and  two 
inches  in  diameter,  one  end  of  which  is  closed  by  a  double  image-prism  of  Iceland 
spar,  and  the  other  by  a  plate  of  quartz.  Looking  through  the  former  we  see  two 
images  of  the  latter,  which,  when  the  light  is  polarized,  assume  complementary  tints. 
If,  now,  the  corona  was  polarized  in  planes  passing  through  the  center  of  the  sun  (as 
is  generally  admitted)  when  viewed  through  the  polariscope,  in  one  image  the  upper 
and  lower  parts  should  have  appeared  blue  and  those  on  the  right  and  left  yellow; 
while  in  the  second  image  these  colors  would  be  reversed,  the  yellow  being  above 
and  below  and  the  blue  on  the  sides.  In  reality  the  two  images  were  precisely  alike, 
and  both  pure  white,  but  one  was  on  a  blue,  the  other  on  a  yellow,  back  ground. 
From  this  we  may  infer  that  the  corona  was  unpolarized,  or,  at  least,  that  the  polarization 
was  too  slight  to  be  perceptible.* 

Although  this  does  not  prove  that  it  shines  by  its  own  light,  since  polarization  is 
produced  only  by  diffuse  reflection,  yet  these  observations,  and  also  those  with  the 
spectroscope,  seem  to  render  it  probable.  This  view  is  also  strengthened  by  the  fact 
that  as  the  most  distant  portions  are  but  about  one  hundredth  part  of  the  distance  of 
the  earth,  they  receive  over  ten  thousand  times  as  much  heat  per  square  foot. 

The  colored  background  mentioned  above  shows  that  the  sky  close  to  the  corona 
is  strongly  polarized,  and  since  the  tint  is  uniform  on  all  sides  of  the  sun,  the  plane  of 
polarization  is  independent  of  the  position  of  the  latter ;  that  is,  the  same  on  the  sides 
that  it  is  above  or  below  it.  The  most  probable  explanation  of  this  most  unexpected 
result  is  that  the  earth  beyond  the  limits  of  the  shadow  being  strongly  illuminated 
acts  as  an  independent  source  of  light,  and  this  being  reflected  by  the  air  becomes 
polarized  in  planes  perpendicular  to  the  horizon. 

I  am  indebted  to  Mr.  E.  L.  Wilson  for  the  use  of  two  Vogel's  photometers,  and  also 
to  Messrs.  Hover  and  Leisenring  for  assistance  in  the  photographic  experiments. 

In  conclusion,  the  new  facts  elicited  may  be  summed  up  as  follows :  An  increase 
of  heat  and  actinic  power  is  observed  in  the  beginning  of  the  eclipse,  caused  by  an 
increased  brightness  of  the  sun's  disk  near  the  moon's  limb.  The  spectrum  of  the 
corona  appears  to  be  free  from  dark  lines,  but  may  contain  two  or  three  bright  ones. 
Its  striae  are  spiral  rather  than  radial,  and  its  light  is  unpolarized.  The  sky  adjoining 
it,  however,  reflecting  light  from  the  earth,  shows  strong  signs  of  polarization. 

Respectfully  submitted. 

EDWARD  C.  PICKERING. 

*  A  similar  result  was  obtained  with  this  instrument  in  1870  by  Mr.  Waldo  O.  Ross  (U.  S.  Coast  Survey  Report, 
1870,  p.  173).  In  1878  Mr.  W.  H.  Pickering  obtained  a  different  result  (Monthly  Notices  Roy.  Astron.  Soc.,  XXXIX, 
138).— E.  C.  P. 

13  ES 


98  ECLIPSE  OP  THE  SUN  AUGUST  7,  1869. 

NOTE  ON  THE  SUPPOSED  POLARIZATION  OF  THE  COKONA.* 

BY  PROF.  E.  C.  PICKERING. 

An  observation  on  this  subject  is  given  in  my  report  on  page  285  of  the  current 
volume  of  this  Journal,  but  as  the  form  of  the  instrument  used  has  been  in  one  or  two 

cases  misunderstood,  I  inclose  a  sketch  of  it.  A  B 
(Fig.  i)  is  a  sheet-iron  tube,  closed  at  A  with  a  plate 
of  quartz  and  at  B  with  a  prism  of  Rochon.  The 
latter  has  the  property  of  giving  two  images  of  any 
object  seen  through  it,  separated  by  an  angle  of  nearly  3°.  Looking  through  the 
tube  we  therefore  see  two  images  of  the  quartz  touching,  but  not  overlapping.  When 
the  light  is  polarized  these  images  assume  complementary  tints,  which  vary  with  the 
plane  of  polarization  and  the  thickness  of  the  quartz.  On  turning  this  instrument 
towards  the  sun  during  totality,  the  images  presented  the  appearance  shown  in  Fig.  2. 
The  hexagons  represent  in  form  and  size  the  plate  of  quartz;  the  black  circles 

the  moon,  here  drawn  a  sixth  of  an  inch  in  diameter, 
as  the  scale  is  about  3°  to  the  inch.  The  corona 
appeared  white,  but  the  sky  surrounding  it  was 
colored  in  one  image  blue,  in  the  other  yellow, 
represented  in  the  figure  by  vertical  and  horizontal 
lines.  The  conclusion  to  be  drawn  from  this  is,  that 
the  light  of  the  corona  is  unpolarized,  or,  more 
strictly,  that  the  amount  of  polarized  light,  if  any, 
is  too  slight  to  be  perceptible  with  this  instrument. 
Its  delicacy,  although  not  equal  to  Savart's  polariscope,  is  very  great,  giving  colored 
images  with  paper,  wood  and  other  bodies  which  reflect  a  small  amount  of  light 
specularly.  The  day  before  the  eclipse  it  showed,  in  a  very  marked  manner,  the 
polarization  of  the  wet  pavements  and  roofs.  To  measure  its  sensitiveness,  I  viewed 
the  light  reflected  by  a  piece  of  plate  glass,  at  different  angles  of  incidents,  and  found 
that  the  color  ceased  to  be  visible  when  this  angle  was  about  10°,  which,  allowing  for 
the  reflection  from  the  second  face,  would  give  about  one  part  of  polarized  to  twenty- 
four  of  natural  light. 

Observers  heretofore  have  generally  attached  their  polariscope  to  a  telescope, 
and  thus  introduced  a  source  of  error,  avoided  in  my  instrument.  For,  light 
passing  through  the  object-glass  and  field  lens  would  be  polarized  by  refraction  before 
reaching  the  polariscope  by  the  obliquity  of  the  incidence,  caused  both  by  the  curva- 
ture of  the  surfaces  and  the  fact  that  the  edge  of  the  field  of  view  receives  its  light 
not  parallel  to  the  axis.  The  plane  of  polarization  would  be  perpendicular  to  a  plane 
falling  through  the  axis  of  the  instrument.  Now,  if  any  part  of  the  corona  was 
brought  into  the  center  of  the  field  of  view,  the  adjoining  portions  would  appear 
polarized  in  planes  parallel  to  the  edge  of  the  field,  or  passing  through  the  sun's  center. 
In  sweeping  around  the  sun's  edge  the  plane  of  polarization  would  continually  change, 

•From  Journal  of  the  Franklin  Institute,  Iviii,  372. 


EEPORT  OF  PEOF.  B.  C.  PICKERING.  99 

as  the  corona  passed  through  different  parts  of  the  field,  and  the  comparative  darkness 
of  the  moon's  disk  and  the  exterior  sky  prevent  the  polarization  of  the  other  portions 
of  the  field  from  being  visible.  The  degree  of  polarization  by  refraction  would  be 
very  slight  and  perhaps  imperceptible,  but  the  agreement  of  observation  with  this 
hypothesis  is  certainly  a  curious  coincidence. 

The  strongest  argument  against  the  polarization  of  the  corona  is  furnished  by  the 
spectroscope,  the  presence  of  bright  lines  and  absence  of  dark  ones,  as  observed  by 
Prefessor  Young,  denoting  incandescence,  a  view  strengthened  by  the  consideration 
that  each  square  centimeter  of  the  surface  of  the  corona  would  receive  several 
thousand  units  of  heat  per  minute.  I  am  well  aware  that  my  results  are  at  variance 
with  those  obtained  by  previous  observers,  including  some  of  the  most  eminent 
astronomers  of  the  day,  but  as  far  as  I  can  learn  this  form  of  polariscope  has  not  been 
used  for  the  purpose,  and  therefore  hope  that  my  experiment  may  be  repeated  during 
the  next  eclipse. 

[NOTE. — Since  writing  the  above  I  learn  from  Prof.  F.  H.  Smith  that  an  excellent  Arago's  polariscope  was  used 
at  Eden  Ridge,  Tenn.,  in  observing  the  eclipse.  The  result  agreed  with  mine,  namely,  that  no  traces  of  polarization 
could  be  detected  in  the  corona  with  this  instrument]. — E.  C.  P. 


REPORT 


OF 


PROF.    STEPHEN    ALEXANDER, 

OTTTJMWA,    IOWA.. 


101 


REPORT  OF  PROFESSOR  STEPHEN  ALEXANDER. 


OBSERVATIONS  AT  OTTUMWA,  IOWA. 

COLLEGE  OF  NEW  JERSEY,  Princeton,  December,  1869. 

SIR:  Having  as  astronomer  occupied  one  of  the  stations  which,  in  your  official 
capacity,  you  had  selected  for  the  observation  of  the  total  eclipse  of  the  sun  of  August 
7,  1869,  I  beg  leave  respectfully  to  report: 

That  after  special  consultation  with  yourself,  at  Burlington,  Iowa,  I  fixed  upon 
Ottumwa  as  my  own  place  of  observation,  because  of  its  special  advantages  for  our 
purpose.  On  the  day  of  the  arrival  there  of  myself  and  assistants,  i.  e.,  August  2,  I, 
in  company  with  my  assistant,  Gen.  Norris  Halsted,  made  choice  of  a  station  on  an 
eminence  about  a  mile  and  a  quarter  to  the  northeast  of  the  center  of  the  city ;  the 
station  being  indeed  one  of  several  which  had  been  personally  inspected  by  you 
several  days  before.  From  it  we  had  an  unobstructed  view  of  the  whole  circumfer- 
ence of  the  horizon  except  a  small  portion  toward  the  northeast. 

I  forthwith  made  arrangements  for  the  construction  of  a  temporary  observatory 
for  the  accommodation  of  the  photographic  party,  which  was  to  be  stationed  at  the 
same  place,  in  accordance  with  your  own  arrangements;  the  construction,  position, 
&c.,  of  the  observatory  being  all  in  accordance  with  the  plan  prescribed  by  yourself. 
Associated  with  me  as  assistants  were  Gen.  Norris  Halsted,  of  Kearney,  N.  J.;  and 
Mr.  Thomas  L.  Graham,  of  Pennsylvania ;  and  as  supernumeraries,  four  members  of 
the  senior  class  in  the  college  of  New  Jersey,  viz:  George  H.  Hooper,  Charles  H. 
Moore,  John  E.  Peters,  of  New  Jersey,  and  George  C.  Yeisley,  of  Maryland. 

We  had  with  us  4  mounted  telescopes,  besides  field-glasses;  my  own  being  an 
achromatic  refractor  by  Utschneider  and  Fraunhb'fer,  aperture  nearly  3  English  inches, 
and  focal  distance  of  object-glass  5 1  inches.  I  had  with  me  a  filar  micrometer  adapted 
to  this.  We  had  also  i  pocket  and  2  box  chronometers,  9  thermometers,  a  Daniels 
hygrometer,  an  aneroid  barometer,  and  2  thermo-electric  piles  with  attached  apparatus. 

We  had,  withal,  the  valuable  co-operation  of  the  photographic  party,  detailed  by 
Professor  Morton  to  occupy  the  Ottumwa  station,  consisting  of  Prof.  Charles  F.  Himes, 
Ph.  D.,  of  Dickinson  College,  Carlisle,  Pa. ;  Messrs.  J.  Zentmayer,  E.  Moelling,  of  Phil- 
adelphia; and  J.  C.  Browne,  of  Buffalo. 

Professor  Himes  has  himself  reported  to  you,  and  also  put  you  in  possession  of 
the  results  which  the  photographers  obtained,  of  which,  it  seems  to  me,  it  may  well 
be  said  that  they  are  unequaled  of  their  kind. 

It  is  here  only  necessary  to  advert  to  some  arrangements  which  we  had  in  common. 
A  chronograph  was  set  up  just  outside  of  the  observatory,  on  which  the  astronomical 

103 


104 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


assistants  (in  turn)  "tapped"  the  seconds  shown  by  the  standard  chronometer  (Daniel's 
g'g),  which  were  also  audibly  called  out,  and  the  minute  also  marked,  as  the  limit  of  60" 
was  reached,  by  the  assistant  specially  charged  with  that  duty.  It  was  also  intended 
that  the  records  of  times  of  the  phenomena  and  those  of  taking  the  photographic  im- 
pressions should  be  marked  on  the  fillet  of  the  chronograph,  each  observer  being 
furnished  with  his  own  key  to  make  connection.  The  success  of  the  arrangement 
was  but  partial,  and  the  other  box  chronometer  (Negus  2335)  was  passed  over  to 
Professor  Himes,  in  the  observatory,  and  by  the  aid  of  it  he  made  his  own  record  of 
the  times  of  taking  the  photographs. 

Observations  for  time  were  obtained  on  the  3d,  4th,  7th,  and  gth  days  of  the 
month.  [The  results  are  incorporated  in  the  table  for  chronometer,  Daniel's  ^,  on  page 
1 6.  The  correction  for  this  chronometer  referred  to  Burlington  mean  time,  August 
7  5b  was  +  5h  57™  6s.  7,*  and  to  Ottumwa  time,  was  assumed  to  be  -f-  5h  52™  o8.  o,  and 
the  hourly  change  +  os.O3.] 

OBSERVATIONS   OF    THE    ECLIPSE. 

The  observed  times  of  the  principal  phenomena  and  the  corresponding  Ottumwa 
times  were  as  follows,' the  names  of  the  observers  being  annexed: 

FIRST  CONTACT. 


Chronometer  time. 

Ottumwa  time.j- 

Observer. 

h.    m.      s. 

h.    m.      s. 

9     57     54-3 

3    49     54-  3 

Alexander. 

57-4 

57-4 

Halsted. 

SECOND  CONTACT. 

Disappearance  of  all  the  sun's  limb,  except  part  broken  into  drops,  which  rather 
seemed  to  adhere  to  the  moon,  as  recorded  on  the  chronograph. 

Chron.  time,  uh  om  498.24;  Ottumwa  time,  4h  52™  498.2.     (Alexander.) 

Total  immersion  of  the  drops,  chron.  time,  nhom  49".44;  Ottumwa  time,  4h  52™ 
4984.  (Alexander.) 

Disappearance  of  two  small  bright  prominences  (flames)  on  the  side  of  the  corona 
toward  which  the  moon  was  advancing,  as  noted  by  Peters  in  his  telescope,  4h  53™  35", 
Ottumwa  time. 

THIRD  CONTACT. 


Chronometer  time. 

Ottumwa  time. 

Observer. 

h.      m.     s. 

h.      m.     s. 

ii       3     40 

4     55     40.  o 

Halsted. 

40.8 

40.8 

Peters.}:. 

*  This  correction  and  Ottumwa  mean  times  of  observations  should  be  diminished  i".5,  p.  16. — C. 
t  Professor  Alexander  thinks  these  times  should  be  lnl  later. — C. 

t  Mr.  Peters  noticed  in  his  telescope  a  manifest  increase  oP  light  near  the  end  of  the  total  eclipse,  along  that 
part  of  the  moon's  limb  where  the  sun  was  about  to  emerge. 


REPORT  OF  PROF.  STEPHEN  ALEXANDER. 

LAST  CONTACT.  * 


105 


Chronometer  time. 

Ottumwa  time. 

Observer. 

h.  m.      s. 

h.    m. 

s. 

o     o     11.3 

5     52 

"•3 

Alexander. 

(or  possibly    12.  o) 

(or 

12.  0) 

12-3 

12-3 

Halsted. 

NOTE. — The  Ottumwa  mean  times  computed  from  the  American  Ephemeris  for  latitude  40°  58'  N.  and  longitude 
ih  jm  2o".7  W.  from  Washington  are  for — 

Beginning  of  eclipse 3h  49™  44'.82 

Beginning  of  totality 4n5im45".58 

End  of  totality 4tS4m36I.i3 

End  of  eclipse 50  5im  I4".92 

The  record  of  the  total  immersion  needs  an  explanation.  The  seconds  had  been 
audibly  called  and  tapped  by  the  assistant  on  the  key  of  the  chronograph  until  within 
a  few  seconds  before  the  total  immersion,  when  the  putting  forth  of  my  hand  to 
obtain  access  to  the  key  when  immersion  should  take  place  was  mistaken  by  the 
assistant  as  a  signal  that  I  meant  to  go  on  with  the  tapping  myself,  and  he  therefore 
stopped  doing  so,  as  well  as  the  calling  of  the  seconds.  The  time  was  not  one  for  expla- 
nations; but  my  own  impressions  of  the  key,  both  when  the  drops  were  all  that  re- 
mained visible  of  the  sun,  and  when  they  disappeared,  have  produced  their  very  distinct 
marks  on  the  fillet  of  the  chronograph,  though  the  taps  for  seconds  failed  to  be  im- 
pressed. The  assistant,  however,  began  his  calling  of  seconds  anew  before  the  occur- 
rence of  the  limit  of  the  next  60",  and  the  termination  of  the  minute  was  marked  on  the 
fillet  by  the  assistant  in  charge  of  that  matter.  The  lengths  due  to  minutes  being  thus 
ascertained,  and  the  interval  of  the  record  of  total  immersion  of  limb  and  that  of  the 
drops  from  the  nearest  minute  mark  carefully  measured,  the  seconds  and  fractions  have . 
been  deduced  from  these  by  proportion;  the  value  of  the  interval  thus  deduced  being 
—  io9.76  for  the  disappearance  of  the  limb,  and — io*.56  for  the  vanishing  of  the  drops; 
the  duration  of  the  drops  after  every  other  portion  of  the  sun  had  disappeared  being, 
as  thus  recorded,  o8.2o.  The  weight  of  the  observation  thus  recorded  is,  of  course, 
diminished  by  the  circumstances  here  detailed,  but  the  result  would  seem  to  be  very 
closely  consistent  with  the  record  of  the  other  phenomena,  and,  among  them,  with  the 
duration  of  the  total  eclipse  due  to  the  position  of  Ottumwa. 

The  corona  and  its  appendages. — The  total  immersion  was  scarcely  complete  f  when 
General  Halsted  earnestly  called  the  attention  of  the  other  observers  to  an  unlocked 
for  and  striking  phenomenon.  The  greater  portion  of  the  corona  appeared  doubled  as 
if  by  reflection;  the  seeming  image  being  to  the  right  of  the  real  and  the  line  joining 
the  centers  of  the  object,  and  this  image  inclining  downward  toward  the  right,  the 
outline  of  the  whole  being  that  of  a  figure  8  turned  very  nearly  sidewise.J  In  color 
and  appearance  the  outline  of  the  strange  appendage  to  the  corona  closely  resembled 

*  These  times  were  im  less  as  first  reported. — C. 

tGeneral  Halsted's  phenomenon  was  seen  just  after  the  total  eclipse  began,  instead  of  just  before,  as  I  learned 
subsequently  by  personal  interview,  but  the  light  was  no  doubt  brighter  on  the  side  where  the  sun  was  last  seen. 

}A  communication  to  the  writer  of  this  report  from  Mr.  S.  Fountain,  postmaster  at  Rocky  Mount,  N.  C.,  states 
that  "during  the  observation  two  rings  were  visible  elongated  east  and  west,  broader  on  the  southern  limb  of  the 
dark  disk  of  the  moon.    Just  under  the  outer  ring  appeared  a  red  spot." 
14  E  S 


106  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

that  of  the  "old  moon  in  the  arms  of  the  new" — that  portion  of  the  border  of  the 
moon  which  is  seen  soon  after  the  new  moon  illuminated  by  earth  light.  The  drawing* 
of  the  appearance  sent  with  this  report  has  been  submitted  to  General  Halsted  and 
approved  by  him.  The  appearance  was  of  very  short  duration. 

The  corona  had  a  clear,  white,  very  brilliant  and  almost  sparkling  appearance, 
its  light  being  very  like  that  of  the  planet  Venus  as  seen  in  the  early  evening  twilight. 
It  had  a  flame-like  outline,  but  the  projecting  portions  were  not  so  far  extended,  nor 
did  they  present  so  great  an  appearance  as  seems  to  have  been  noticed  elsewhere. 
Some  of  the  observers  spoke  of  the  upper  left-hand  portion  on  the  east  limb  as  being 
brighter  than  the  rest  and  also  of  its  being  a  little  wider  there. 

Seven  protuberances  in  all  were  noted,  and  the  enlarged  copy  of  the  photograph 
of  the  "totality,"  (Plate  VII),  shows  protuberances  in  nine  places.  Some  of  these  pro- 
tuberances were  conspicuous  to  the  bare  eye,  and  to  most  of  the  observers  the  colors 
of  these  appeared  to  be  a  lively  red.  Such  was  their  color  as  seen  by  my  own  eye 
on  a  first  inspection.  I  then  turned  away  to  arrange  the  thermo-electric  pile,  arid 
while  the  screen  of  that  was  removing,  examined  the  corona  with  the  telescope.  The 
protuberances  appeared  with  all  the  distinctness  that  is  characteristic  of  so  fine  a 
refractor,  but  at  first  view,  thus  seen,  they  were  white,  and  yet,  within  the  few  seconds 
which  I  could  devote  to  their  inspection,  these  white  prominences,  portions  of  them, 
became  tinted  with  a  pale  rose  color,  so  that  they  appeared  not  unlike  pinnacled 
glaciers  or  icebergs  illuminated  by  the  setting  sun — an  appearance  which  explained 
why  some  European  observers  of  the  total  eclipse  of  1842,  in  their  descriptions,  spoke 
of  the  protuberances  as  "fiery  mountains."  The  lithograph  in  Schumacher's  Astrono- 


misclie  Nachsichten  fur  1843,  vol.  20,  represents  all  this  exceedingly  well.  The  outlines 
of  two  of  those  observed  at  Ottumwa  were  as  they  appeared  to  me,  very  nearly  as 
here  represented,  the  shape  of  the  larger  one  being  withal  justified  by  a  comparison 
with  the  enlarged  copies  of  photographs. 

As  to  the  color  of  the  protuberances,  as  seen  by  some  of  the  other  observers, 
General  Halsted  saw  the  protuberances  red  with  the  bare  eye,  and  also  at  first  with 
his  telescope,  though  they  afterwards  appeared  white.  He  removed  his  eye  from 
the  telescope  to  see  how  that  could  have  happened,  and  when  he  looked  again  with 
the  instrument  the  protuberances  appeared  of  a  rose  color. 

Professor  Himes,  who  wears  glasses,  states  that  "at  the  first  instant  of  totality  my 


"This  drawing,  and  another  subsequently  furnished,  exhibit  two  images  of  the  eclipsed  sun,  that  to  the  right 
being  the  fainter  and  less  distinct,  and  lapping  each  other  about  one-sixth  of  the  diameter  of  each.  It  would  seem 
to  have  been  a  case  of  binocular  vision  but  for  the  implication  that  the  duplication  was  seen  by  more  than  one  person 
The  drawings  show  no  appearance  of  a  corona,  but  only  a  narrow  fringe  of  light.— C. 


REPORT  OF  PROF.  STEPHEN  ALEXANDER.  107 

I 

eyes  were  directed  to  the  moon,  and  I  perceived  dazzling  white  prominences  projecting 
apparently  from  the  moon.  My  attention  was  then  attracted  to  the  photographic 
apparatus,  and  after  about,  half  a  minute,  upon  looking  up  I  found  the  former  white 
prominences  of  a  brilliant  decided  rose  color,  bordering  on  crimson,  and  they  remained 
of  this  color  to  the  close  of  the  totality."  According  to  my  note  of  conversation  with 
him  two  days  after  the  eclipse  he  also  saw  the  protuberances  rose  color  with  a  field- 
glass. 

Mr.  Browne  had  been  confined  to  the  "dark  room"  of  the  photographic  observa- 
atory,  which  was  coated  with  orange-colored  curtains,  and  in  it  were  two  candles 
burning  guarded  by  quite  yellow  tissue  paper.  The  view  which  he  had  at  the  middle 
of  the  totality  lasted  but  for  three  seconds.  Everything  appeared  to  him  as  if  tinted 
with  smoke.  As  seen  with  the  bare  eye  the  protuberances  appeared  white,  bordered 
with  a  delicate  rose  color.  Mr.  Zentmayer  and  Mr.  Moelling  had  been  looking  on  the 
screen-glass  of  the  photographic  apparatus.  Mr.  Zentmayer  last  saw  the  protuberances 
white  with  a  slight  tinge  of  blue.  Mr.  Moelling  saw  them  white  all  the  time.* 

Most  persons  saw  with  the  bare  eye  an  intrusion  of  light  on  the  moon's  disk,  of  a 
nearly  triangular  shape,  issuing  from  the  base  of  a  protuberance.  Especially  was  this 
true  of  the  largest  of  all  of  those  appendages  near  to  the  lowest  point  of  the  moon's 
edge.  In  the  photograph,  Plate  VIII  of  the  totality,  the  place  of  this  is  partly  occupied 
by  a  white  spot  nearly  parallel  to  the  protuberance  and  also  to  another  spot  outside  of 
the  disk.  This  photograph  distinctly  recalls  to  General  Halsted  what  he  saw  in  his 
telescope. 

It  was  in  accordance  with  your  own  suggestion  that  I  endeavored  to  obtain  some 
indication,  if  it  so  might  be,  of  the  heat  of  the  corona.  Disappointed  in  obtaining  a 
lens  of  rock  salt,  I  had  provided  several  convex  lenses  of  glass  of  short  focus,  and 
also  a  concave  mirror  of  9  inches  diameter,  to  concentrate  heat,  and  a  very  sensitive 
thermo-electric  pile  to  indicate  the  effect  of  the  concentration.  It  seemed  right  to  make 
the  experiment,  though  without  the  rock  salt  there  seemed  almost  no  hope  of  success, 
the  mirror  not  being  arranged  for,  as  it  could  not  be  known  beforehand  how  bright 
the  image  of  the  corona  would  be.  The  image  by  refraction  through  a  glass  lens  was 
thrown  on  the  end  of  the  pile  for  a  ver)'  short  time  without  any  sensible  effect,  and 
was  still  held  there  when  the  first  beam  of  sunlight  emerged.  Trying  this  experiment 
interfered  with  even  the  setting  of  the  web  in  the  filar  micrometer  so  as  to  read  off 
afterward  the  measurement  of  the  height  of  the  protuberances,  and  there  was  too  much 
else  doing  to  enable  us  to  make  efficient  use  of  the  Daniel's  hygrometer.  Some  of 
these  things  had  to  be  abandoned,  though  not  without  the  expectation  that  they  would 
be  used  elsewhere,  while  it  was  feared  that  the  attempt  to  obtain  the  heat  of  the  corona 
would  not  elsewhere  be  made. 

OTHER   OBSERVATIONS. 

The  degree  of  darkness  during  the  total  eclipse  was  such  that  large  print  could 
with  difficulty  be  read.  Animals  behaved  as  they  usually  do  when  night  is  coming  on. 

*Mr.  H.  P.  Norton,  of  Moniuouth.  111.,  saw  the  protuberances  red  at  first,  but  white  just  after  the  emersion  of 
sunlight. 


108 


ECLIPSE  OF  THE  SUK,  AUGUST  7,  1860. 


The  increasing  darkness  was  painted  on  the  sky  toward  the  west  some  time  before 
the  total  eclipse,  and  again  the  same  tint  was  visible  eastward  after  the  total  eclipse 
was  over,  and  those  who  were  at  liberty  to  do  so  observed  with  what  frightful  rapidity 
we  were  plunged  into  the  dark  shadow,  and  the  contrary  effect  as  we  emerged  into 
sunlight.  No  wind  was  perceptible  during  the  total  eclipse.  The  white  light  of  Venus 
and  the  ruddy  light  of  Mercury  appeared  in  beautiful  comparison,  and  contrast  as  well, 
as  soon  as  the  sun  was  totally  hidden.  Saturn,  also,  and  at  least  four  fixed  stars,  were 
seen.  Arcturus  appeared  white  to  both  General  Halsted  and  Mr.  Graham. 
The  Ottumwa  times  of  other  miscellaneous  observations  were  as  follows: 


Time. 

Observer. 

A  distortion  of  the  upper  cusp  

}h  IS01  ??• 

Bright  band  bordering  the  moon  near  the  cusps  of  the  eclipsed  sun  . 
Contact  with  a  large  spot  

411      40 

Do. 
Do 

Total  immersion  of  large  spot  

Do 

Emersion  of  two  small  round  spots  

S-JI 

Do 

Bright  band  bordering  the  moon  

5-i(\ 

Do 

Bright  band  bordering  the  moon  

1      dl 

Do 

Bright  band  bordering  the  moon  (seen  very  plainly)  

Do 

Emersion  of  a  long  spot    

Do 

OBSERVATIONS    OF   TEMPERATURE    BY   MR.    YE[8LEY. 

The  thermometers  have  the  initials  of  the  maker's  nameappended:  F.,  for  Faulkner; 
P.,  for  Pike,  and  R,  for  Russell.  Those  designated  by  a  *  were  alcoholic,  the  others 
mecurial  thermometers.  The  degrees  are  those  of  Fahrenheit.  The  dates  are  in  local 
mean  time. 


BBPOET  OF  PEOF.  STEPHEN  ALEXANDER. 

Thermometers. 


109 


1869. 

In  sun. 

In  shade. 

August  7. 

P. 

P.* 

R. 

R. 

P.* 

P. 

P. 

F. 

F.* 

Remarks, 

h.  m. 

0 

0 

O 

0 

0 

O 

0 

O 

o 

2   10 

93 

91 

72 

72 

72 

72 

72 

74 

73 

20 

9" 

92 

72 

72 

72 

74 

74 

74 

73 

3° 

90    91 

7' 

7" 

72 

72 

74 

74 

74 

40 

90    91 

7' 

7« 

72 

72 

74 

74 

74 

5° 

92 

93 

7° 

7° 

72 

74 

74 

74 

74 

"?     o 

96 

95 

70 

7i 

72 

74 

74 

74 

74 

IO 

96 

95 

7' 

72 

72 

74 

74 

74 

74 

20 

96 

96 

7i 

72 

72 

74 

74 

74 

74 

30  \ 

Thermometers  moved. 

40  / 

5° 

90 

9' 

7° 

72 

72 

73 

73^ 

73'/2 

73^ 

Beginning  of  eclipse. 

4   o 

gg 

90 

70 

7i 

7« 

72 

73 

73 

73 

10 

86 

88 

69 

70 

72 

72 

72^ 

72^ 

72^ 

20 

84 

85 

69 

70 

70 

72 

72 

72 

72 

3° 

76 

78* 

68 

68 

69 

70 

70 

7' 

7' 

4° 

5° 

7° 

7' 

65 

66 

68 

68 

6g 

68 

68 

Before  totality. 

5   ° 

67 

68 

64 

65 

68 

68 

6g 

68 

68 

After  totality. 

10 

70 

7i 

64 

64 

65 

66 

66^ 

68 

68 

20 

74 

75 

64 

64 

65 

66 

68 

68 

68 

3° 

73 

76 

66 

66 

65 

68 

68 

68 

68 

40 

78 

80 

64 

64 

66 

66 

68 

68 

68 

50 

78 

80 

64 

66 

66 

68 

68 

68 

68 

End  of  eclipse. 

6   o 

74 

75 

64 

64 

66 

67 

68 

68 

68 

Barometric  observations  by  Mr.  Peters. 

These  may  be  useful  as  indicating  to  some  extent  the  changes  of  the  aneroid 
barometer  which  was  used,  its  index-error  not  having  been  determined. 


ig69. 

An.  barometer. 

Ig6g. 

An.  barometer. 

Remarks. 

h.  m. 

in. 

h.   m. 

in. 

August  5.      6    o  a.  m. 

29.25 

August  7.      3  15  p.  m. 

29-44 

5  45  P-m- 

.  22 

3  3°  P-  "»• 

•  44 

6.     5  30  a.  m. 
2  10  p.  m. 

.  20 
•3' 

3  45  P-  m. 
4     o  p.  m. 

•  42 
•42 

Beginning  of  eclipse. 

7.      703.  m. 

.48 

4  15  P-  m- 

•42 

g  30  a.  m. 

•5° 

4  30  p.  m. 

.42 

i     o  p.  m. 

.48 

4  45  p.  m. 

.42 

2     o  p.  m. 

.46 

5    o  p.  m. 

.40 

Total  eclipse. 

2  15  p.  m. 

.46 

5  15  p.m. 

.40 

2  30  p.  m. 

•44 

5  3°P-m- 

.40 

2  45  p.  m. 
3    o  p.  m. 

•44 
•  44 

5  45  P-  m- 
6    o  p.  m. 

.40 
29.40 

End  of  eclipse. 

110  ECLIPSE  OP  THE  SUN,  AUGUST  7,  1869. 

OBSERVATIONS    FOE   LATITUDE    OF  OBSERVATORY   HILL,  OTTUMWA. 

These  have  been  exclusively  confined  to  altitudes  of  the  sun;  and  because  of 
his  northern  declination,  were  obliged  to  be  more  extra-meridian  than  was  at  all 
desirable.  But  the  interruptions  occasioned  by  the  whole  two  days'  storm  of  the  5th 
and  6th  of  the  month,  and  clouds  and  other  interruptions  at  night  afterwards,  pre- 
vented any  successful  observations  north  of  the  zenith,  except  one  of  Polaris,  and  that 
ill-conditioned.  The  results  consequently  must  be  affected  by  error  in  centering  of 
sextant,  as  well  as  some  uncertainties  of  refraction,  &c.  Eight  observations  of  the  alti- 
tude of  the  sun's  lower  limb,  on  the  4th  of  the  month,  gave  for  the  latitude, 

+  40°   58'   33".o; 
and  ten  observations  of  altitude  of  the  upper  limb  gave  for  the  latitude, 

+  40°    58'   21^.45* 

half  weight  being  allowed  to  two  observations  in  each  case,  which  differed  unduly 
from  the  mean. 

The  mean  of  both  results  is: 

+  40°   58'   27"-2; 

and  the  same  is  the  mean  of  the  whole  eighteen  observations.  Yet  four  observations 
of  the  lower  limb  and  three  of  the  upper  limb  on  the  gth  give  a  mean  of  41  °  o'  22" ;  two 
other  observations  being  rejected  for  their  great  discrepancy  from  the  means  of  the 
others. 

The  double  altitudes  were  in  this  case  near  to  the  extreme  limit  of  1 20°,  where 
the  arc  may  have  been  slightly  bent,  or  its  graduation  faulty.  It  is,  moreover,  possible 
that  the  bottom  of  the  basin  containing  the  oil  used  to  give  the  artificial  horizon  may 
have  interfered  by  its  reflection,  as  it  was  not  everywhere  sufficiently  blackened.  The 
pent-house  [roof]  covering  the  horizon  has  been  tested,  without  an  indication  of  any 
marked  discrepancy,  when  ends  are  interchanged  in  their  position  with  regard  to  the 
observer. 

When  the  times,  by  single  altitudes,  are  separately  computed  and  compared  (as 
they  have  been  largely  for  different  days)  with  those  deduced  by  corresponding  alti- 
tudes, the  latitude  deduced  on  the  4th  being  employed,  the  coincidence  is  close  (the 
effect  of  the  error  in  centering  being  nearly  the  same  for  both). 

The  first  result  (the  mean  of  observations  on  the  4th)  seems  to  be  preferable ; 
and  as  far  as  these  necessarily  imperfect  determinations  can  indicate  we  should  not 
admit  the  latitude  of  our  position  to  be  greater  than  40°  59',  or  that  of  the  center  of 
the  city  more  than  40°  58^'.  Its  latitude  by  estimate,  heretofore,  seems  to  have  been 

41°  3' or  4'. 

The  report  of  the  comparison  with  Burlington  of  telegraphic  signals  for  longitude 
has  been  already  transmitted.! 

Very  respectfully,  your  obedient  servant, 

STEPHEN  ALEXANDER, 

PRINCETON,  December,  1869. 
Prof.  JOHN  H.  C.  COFFIN, 

Superintendent  American  Ephemeris  and  Nautical  Almanac. 

"The  result  from  double  altitudes  for  time  is  given  hereafter. — C. 
tTho  results  are  included  in  tables  on  pages  16  and  17. 


SUPPLEMENTAL  REPORT  BY  PROF.  J.  H.  C.  COFFIN. 

OBSERVATIONS    FOR   TIME    AND   LONGITUDE    OP    OTTUMWA. 

Professor  Alexander's  observations  for  time  at  Ottumwa  were  made  with  a  sextant 
and  artificial  horizon.  Each  set  consisted  of  altitudes,  of  each  limb  and  the  center  of 
the  sun,  observed  with  the  same  reading  of  the  sextant.  The  index  correction 
-25'  13",  found  by  coincidence  of  the  direct  and  reflected  images  of  the  sun,  was 
regarded  as  constant.  The  P.  M.  observations  of  each  day  were  in  part  of  the  same 
altitudes  as  the  A.  M.  observations.  I  have,  however,  reduced  all  the  observations 
separatelv  with  the  assumed  latitudes  +40°  58'  30". 

August  3.  Five  sets  A.  M.  and  two  sets  P.  M.  observations. 

To  reconcile  the  A.  M.  observations,  it  is  necessary  to  suppose  the  sextant  reading  of  the  1st  set  to  be  1'  too 
small,  and  of  the  3d  and  4th,  to  be  1'  too  great.  The  two  sets  of  P.  M.  observations  can  be  reconciled  by  supposing 
the  sextant  reading  of  the  1st  sot,  which  corresponds  to  the  2d  A.  M.  set,  to  be  1'  too  great.  The  A.  M.  and  P.  M.  ob- 
servations may  then  be  more  fully  reconciled  by  diminishing  the  latitude  42",  or  the  altitudes  14". 

August  4.  Five  sets  of  A.  M.  and  five  sets  of  corresponding  P.  M. 

The  P.  M.  observations  agree  if  the  sextant  reading  for  the  2d  set  is  supposed  to  be  1'  too  great,  and  that  for 
the  5th  to  be  1'  too  small.  The  A.  M,  and  P.  M.  observations  are  further  reconciled  by  diminishing  the  latitude  35",  or 
the  altitudes  8". 

August  7.  Six  sets  of  altitudes  were  observed  at  10  a.  m. 

These  observations  give  as  the  correction  of  Chronometer  Daniels  yfo,  -f  5°  52'  2".0  +  O.060  A  L  +  OM07  A 
A,  A  L  and  A  h  being  corrections,  respectively,  of  the  latitude  and  altitudes  in  seconds. 

August  9.  Five  sets  of  A.  M.  and  four  sets  of  P.  M.  observations. 

They  are  reconciled  by  supposing  the  sextant  readings  for  the  5th  A.  M.  and  the  corresponding  1st  P.  M.  sets 
to  be  each  1'  too  small ;  and  more  closely  agree  by  diminishing  the  latitude  24",  or  the  altitudes  8". 

Occasionally  on  each  day  there  was  obviously  an  error  of  io8  in  noting  time, 
which  has  been  corrected. 

Correcting  the  altitudes  as  indicated,  the  latitude  found  by  combining  the  A.  M. 
and  P.  M.  observations  is: 

August  3,  +  40°  57'   48" 
4,  57     55 

9,  58       6 


Mean,         +  40°  57'    56" 

This  combined  with  +  40°  58'  27",  obtained  by  Professor  Alexander  from  his 
observations  for  latitude  on  August  4  (page  i  io),  gives  as  the  concluded  latitude  of  the 
eclipse  station,  -f  40°  58'  12". 

The  following  are  the  results  of  the  time  observations  (that  for  August  7  being 
corrected  for  A  L  —  —  18"),  combined  with  the  chronometer  corrections  in  the  table, 
page  r6;  found  by  comparisons  with  Hutton  202. 


112 


ECLIPSE  OP  THE  SUN,  AUGUST  7,  1869. 

Chronometer  Daniels  j-fy. 


Date. 

Corrections  referred  to 
Ottumwa  mean  time. 

Corrections  referred  to 
Burlington  mean  time. 

Longitude  from  Bur- 
lington. 

h. 

h.  m.      s. 

h.  m.    s. 

m.     s. 

August  3     o 

+  5  51   54-  2 

+  5  57  2-9 

5    8-7 

4     o 

57.6 

4-5 

6.9 

6       22 

60.  9 

5-9 

5.0 

9     o 

61.7 

8-3 

6.6 

Giving  half  weight  to  August  3  and  August  6,  the  mean  difference  of  longitude 
is  5  68.8,  Ottumwa  W.  of  Burlington. 

From  comparisons  of  Chronometer  Negus  2335  with  Daniels  ~,  and  from  the 
table  p.  1 7,  using  the  variable  rate  stated  at  the  bottom,  the  longitude  deduced  is  5m  7".  0. 
But  as  this  is  not  independent  of  that  from  Chron.  -^  and  the  rate  of  2355  is  quite 
irregular,  I  have  adopted — 

Ottumwa,  oh  5m  6".8  west  of  Burlington, 

i     i    20.5    •=.  15°   20'  8"     west  of  Washington. 
6    9    32.6         92     23    9      west  of  Greenwich. 

J.  H.  C.  COFFIN. 


It  E  P  OUTS 


PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 


PltOF.    HENRY    MORTON. 

PEOF.    A.   M.    MEYER, 

liurlington,  Iowa. 

PEOF.    C.    F.    HIMES, 

Ottumwa,  Iowa. 


113 

15  E  s 


REPORTS  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.* 

REPORT  OF   PROF.  HENRY  MORTON,  Ph.  D. 

'.  PHILADKLPHIA,  August  18,  1869. 

SIR:  On  receipt  of  your  letter  of  May  3,  in  which  you  proposed  that  I  should 
undertake  the  organization  and  conduct  of  a  party  to  make  photographic  observations 
of  the  total  eclipse  of  August  7,  I  proceeded  to  make  inquiry  as  to  the  material  which 
might  be  available  for  the  purpose  and,  in  concert  with  and  assisted  by  yourself  and 
Prof.  E.  0.  Kendall,  found  that  \ve  might  readily  procure  two  fine  Munich  Equatorials 
of  6-inch  aperture,  and  with  clockwork,  belonging,  respectively,  to  the  high  school  of 
this  city  and  the  Pennsylvania  College  at  Gettysburg,  and  also  an  excellent  Dollond 
of  4-inch  aperture  equatorially  mounted,  but  without  clockwork,  belonging  to  the 
University  of  Pennsylvania,  in  this  city. 

On  further  consultation  with  yourself,  it  was  concluded  that,  on  account  of  the 
risk  of  local  clouds,  it  would  be  desirable,  if  possible,  to  take  all  these  instruments  and 
distribute  them  over  some  distance  on  or  near  the  central  line. 

On  careful  reflection,  I  came  to  the  conclusion  that  at  least  five  skilled  operators 
would  be  necessary  to  each  instrument,  and  that,  therefore,  something  must  be  done 
to  diminish  the  expense  of  transportation,  or  the  Government  appropriation  available 
for  this  department  of  the  general  eclipse  observations  would  be  insufficient. 

It  also  appeared  that  some  arrangement  by  which  trans-shipment  of  the  numerous 
weighty  and  delicate  pieces  of  apparatus  might  be  avoided  would  be  highly  condu- 
cive to  success  and  security. 

I  therefore  called  upon  my  friend,  Mr.  R.  H.  Lamborn,  secretary  of  the  American 
Steel  Manufacturing  Company,  whose  extensive  connection  with  our  great  lines  of 
interior  transportation  would  give  him  opportunity  of  affording  the  best  advice,  and 
explained  to  him  my  ideas.  He  went  with  me  at  once  to  Col.  Thomas  A.  Scott,  vice- 
president  of  the  Pennsylvania  Central  Railroad,  and  stated  the  case  to  him  with  ad- 
mirable brevity  and  precision. 

Colonel  Scott,  with  the  greatest  kindness,  acceeded  at  once  to  our  request,  and 
promised  to  provide  us  with  a  special  car,  from  which  some  seats  should  be  removed 
to  accommodate  our  apparatus,  and  which  should  go  with  us  to  the  end  of  our  route, 
and  there  remain  until  our  return.  Free  transportation  over  the  entire  route  of  the 
Pennsylvania  Central  and  Fort  Wayne  Railroads  (i.  e.,  as  far  as  Chicago)  for  our 
party,  and  several  others  besides,  was  included  in  or  added  to  this  generous  gift. 

I  then  wrote  to  Mr.  Robert  Harris,  of  Chicago,  general  superintendent  of  the 
Chicago,  Burlington  and  Quincy  Railroad,  asking  him  to  forward  our  car  and  its  con- 
tents over  the  road  in  his  charge.  To  this  he  also  most  kindly  agreed,  and,  although 

"  These  reports  were  published  iu  the  Journal  of  the  Franklin  Institute  for  September  and  October,  1869,  and 
are  here  reproduced  with  revisions  made  in  January,  1871.     All  additions  and  important  changes  are  noted. — C. 

115 


116  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

it  will  anticipate  subsequent  events,  I  may  as  well  say  in  this  place  that  this  gentleman 
also  facilitated  our  movements  in  every  way,  sending  a  locomotive  to  meet  us  at  the 
intersection  of  his  road  with  the  Pittsburgh,  Fort  Wayne  and  Chicago  line,  and  carrying 
us  to  the  depot  for  Burlington  on  our  way  out,  and  transferring  our  vehicle  again  on 
our  return  journey.  Mr.  Norton,  from  Mr.  Harris's  office,  also  met  us  at  the  junction, 
to  explain  the  proposed  disposition,  and  kindly  acted  as  our  guide  through  the  city. 

Provision  being  thus  made  for  transportation,  by  which  an  expense  of  about  $1,500 
was  spared  to  the  Government  appropriation,  the  plan  of  taking  out  a  triple  party 
became  feasible,  and  was  accordingly  adopted. 

The  next  point  was  the  selection  of  the  party,  and  this  was  proceeded  with  at 
once,  communications  being  exchanged  with  many  of  our  leading  photographers  and 
others,  to  learn  their  views  and  inclination.  It  was  soon  found  that  an  excellent  selec- 
tion might  be  had  from  among  those  whose  position  or  engagements  would  allow  them 
to  volunteer  without  other  compensation  than  the  moral  one  contingent  on  success, 
and,  after  a  few  changes  rendered  necessary  by  sickness  or  other  inevitable  cause,  the 
party,  as  finally  constituted,  consisted  of  Prof  A.  M.  Mayer,  Ph.  1).;  Prof.  C.  F. 
Himes,  Ph.  D.;  Messrs.  J.  Zentmayer,  O.  H.  Willard,  E.  L.' Wilson,  H.  C.  Phillips,  E. 
Moelling,  J.  C.  Browne,  W.  J.  Baker,  James  Cremer,  H.  W.  Clifford,  O.  H.  Kendall, 
J.  Mahoney,  W.  V.  Ranger. 

We  were  also  joined,  as  volunteers,  on  the  ground,  by  Mr.  John  Carbutt,  of 
Chicago,  and  Mr.  Miles  Rock,  of  Bethlehem,  Pa.,  and  Mr.  Leisenring,  of  Burlington. 
Professor  Coffin  having  suggested  that  some  general  physical  observations  should  be 
carried  out  in  connection  with  this  party,  I  applied  to  Prof.  E.  C.  Pickering,  of  the 
Massachusetts  Institute  of  Technology,  Boston,  who  consented  to  take  charge  of  these, 
and  accompanied  us  to  Mount  Pleasant,  Iowa,  as  will  be  seen  from  a  subsequent  por- 
tion of  this  report.  Prof.  James  McClune,  of  the  Philadelphia  Central  High  School, 
and  Prof.  S.  G.  Gummere,  also  accompanied  the  expedition,  and  were  stationed  at 
Oscaloosa. 

The  next  point  to  which  attention  was  directed,  was  the  arrangement  of  the  instru- 
ments for  their  photographic  work.  It  was  a  question  of  much  moment  to  decide 
whether  we  would  follow  the  plan  adopted  by  the  French  and  German  expeditions  of 
last  year,  and  make  the  photograph  iTl  the  principal  focus  of  the  object-glass,  thus 
securing  great  intensity  of  light  in  a  small  image,  or  follow  the  method  employed  by 
De  la  Rue  in  1 860,  when  he  used  an  ordinary  Huygenian  eye-piece  so  placed  as  to 
produce  an  enlargement  of  the  first  image  from  the  objective. 

After  a  careful  study  of  De  la  Rue's  report  and  pictures,  as  also  those  of  the  later 
expeditions,  I  came  to  the  conclusion  that  the  plan  of  enlargement  presented  many 
advantages,  and  should  be  followed  by  us  with  certain  modifications,  which  I  will 
proceed  to  describe 

The  work  of  designing  and  constructing  these  lenses,  and  also  the  different  attach- 
ments to  the  cameras  for  securing  exposures  of  various  degrees  of  rapidity,  from  a 
very  small  fraction  of  a  second  to  any  desired  length,  was  placed  in  the  hands  of  Mr. 
Joseph  Zentmayer,  whose  extended  scientific  attainments,  combined  with  unrivaled 
skill  in  the  construction  of  optical  instruments,  peculiarly  fitted  him  for  such  a  task. 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 


117 


The  camera,  as  finished,  is  represented  in  the  accompanying  woodcut,  which  shows 
it  as  seen  from  directly  in  front. 

Here  A  is  represents  the  face-plate  of  the  camera,  to  which  the  eye-piece  tul>e  was 
attached,  its  other  end  being  screwed  to  the  telescope.  The  diaphragm  plate  D  E, 
moved  across  the  axis  of  the  instrument,  being  drawn  downwards  by  the  combined 
spring  E  K.  The  strength  of  this  spring  could  be  reduced  by  raising  the  outer  end  of 
one  or  both  the  upper  strips  so  as  to  disengage  the  forks  at  their  end  from  the  lower 
spring,  and  then  turning  them  forward  in  a  direction  normal  to  the  front  of  the  box, 
out  of  the  way. 


The  spring  was  attached  to  the  diaphragm  plate  by  a  swivel  hook,  which,  while 
in  no  instance  falling  out,  could  be  detached  and  readjusted  with  the  greatest  facility. 

A  number  of  diaphragm  plates  were  provided,  with  slits  respectively  of  -i,  ~,  -i, 
and  ^  of  an  inch  in  width.  These  plates  could  be  readily  interchanged,  and,  in 
combination  with  the  springs,-  gave  a  very  wide  and  yet  delicate  series  of  fixed 
adjustments  for  the  times  of  exposure. 

To  make  the  exposure,  the  plate  was  drawn  up  until  the  projecting  pin  D  could 
be  caught  on  the  lever  K,  which  would  then  retain  it.  On  depressing  the  outer  end 
of  this  lever,  however,  with  the  finger,  the  hold  on  the  pin  was  disengaged,  and  the 
plate  flashed  across  the  axis_of  the  tube,  allowing  light  to  traverse  the  narrow  slit  as 
it  flew  past.  The  plate  was  then  arrested  on  the  end  of  the  second  lever  G.  When 
an  exposure  of  some  seconds  was  required,  as  during  the  totality,  a  plate,  having  a  round 
orifice  exposing  the  entire  field  of  the  eye-piece  was  substituted  for  the  one  with  the 
narrow  slit,  and  was  so  arranged  that,  when  caught  by  the  upper  lever,  it  covered  the 
lens,  but  when  fallen  to  the  second  lever  exposed  it  entirely;  when,  however,  this 
lever  was  in  turn  touched,  the  plate  descended  again  far  enough  once  more  to  close  the 
lens.  By  touching  these  two  levers  in  succession  it  was  then  possible  to  make  a  "time 


118  ECLIPSE  OP  THE  SUN,  AUGUST  7,  18C9. 

exposure"  with  great  nicety  and  accuracy,  as  proved  by  actual  experience  during  the 
eclipse. 

To  secure  a  chronographic  record  of  each  exposure  a  binding  screw  was  provided, 
to  make  one  connection  with  the  general  mass  of  the  face-plate,  including  lever  K,  and 
another  at  L,  to  carry  on  the  circuit  when  the  downward  motion  of  the  lever  brought 
the  spring  at  its  side  in  contact  with  the  point  projecting  from  L.  In  raising  the  lever 
for  a  new  exposure,  the  spring  at  its  side  was  pressed  back  so  as  to  pass  the  point 
without  contact.  A  more  substantial  break-piece  would  have  been  made  had  time 
allowed,  but  this  was  found  to  operate  in  a  perfectly  satisfactory  manner. 

As  the  operation  of  the  eye-piece,  when  employed  to  produce  an  image  on  the 
screen  or  ground  glass  of  a  camera,  is  essentially  different  from  that  which  it  performs 
in  its  usual  office,  it  was  judged  best  by  Mr.  Zentmayer  to  make  some  alterations  in 
its  form.  Thus,  in  the  first  place,  since  in  the  present  case  the  ."eye-lens"  of  the  eye- 
piece undoubtedly  makes  a,  secondary  image  of  the  primary  image  formed  within  the 
eye  piece  by  the  combined  action  of  the  objective  and  the  field  lens  of  the  eye-piece, 
it  is  clearly  desirable  to  make  this  lens  of  a  longer  focus  than  usual,  so  that  its  errors 
may  be  of  less  account.  It  was  also  essential  to  give  the  new  eye-piece  a  wide  angle, 
so  as  to  secure  a  sufficient  field  not  only  for  the  solar  disk,  but  also  for  the  corona. 

While,  therefore,  the  ratio  of  focal  lengths  in  the  two  lenses  of  the  ordinary  eye- 
piece is  usually  1-3,  it  was  in  this  case  as  1-2.  While  the  distance  between  the  lenses 
is  usually  the  sum  of  their  focal  lengths  divided  by  2,  it  was  here  made  equal  to  the 
sum  of  the  focal  lengths  divided  by  2  plus  .24  inch.  This  was  to  give  space  for  the 
introduction  of  the  reticule  of  spider-lines,  which  would  otherwise  have  been  brought 
too  near  the  field  lens,  and  also  to  keep  this  lens  beyond  the  conjugate  focus  of  the 
eye  lens,  as  otherwise  particles  of  dust  on  the  former  would  have  been  too  faithfully 
portrayed  by  the  latter. 

The  elements  actually  adopted  were  as  follows: 

ft.  in. 

Focal  length  of  objective 8  6. 

Radius  of  field  lens '-375 

Radius  of  eye  lens 0.687 

Focus  of  field  lens 2.6 

Diameter  of  field  lens  (zrR) 1-375 

Focus  of  eye  lens 1.3 

Diameter  of  eye  lens  (  zzR) 0.687 

Distance  between  lenses,  1.95+0.25 2.2 

Equivalent 1.75 

Distance  of  reticule  from  eye  lens  for  5-inch  distance  of  ground  glass  .  1.62 

The  reticule  was  mounted  on  a  short  tube  with  a  fine  thread  on  the  outside 
running  in  a  corresponding  thread  on  the  inside  of  the  eye-piece  tube.  This  being 
approximately  adjusted  beforehand,  was  moved  to  its  exact  place  by  turning  it  with  a 
sharp  point  through  a  little  slot  cut  in  the  eye-piece  tube. 

One  of  the  cameras  with  its  eye-piece,  being  finished,  experiments  were  at  once 
made  with  the  telescope  of  the  University  of  Pennsylvania,  which,  by  reason  of  its 


KKL'OliT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.          119 

smaller  size,  was  most  readily  available  for  such  purpose.  These  were  conducted  by 
Mr.  Willard,  Mr.  Zentmayer,  and  myself,  at  the  establishment  of  Mr.  Willard,  1 206 
Chestnut  street,  where  all  conveniences  for  the  work  were  at  hand,  and  were  of  the 
greatest  value  in  affording  data  on  which  the  construction  of  the  other  apparatus  could 
be  based. 

It  was  found  that,  with  a  clear  sun,  it  was  necessary  to  reduce  the  ap*erture  of  this 
telescope  (which  was  4  inches,  with  50  inches  focus),  to  if>  inches,  and  to  use  all  three 
springs  and  the  diaphragm-slide  of  /„  inch  aperture,  in  order  to  get  a  proper  exposure 
when  the  solar  image  was  enlarged  from  6.  incli  (its  diameter  at  the  principal  focus  of 
the  objective)  to  2\  inches  on  the  ground  glass.  The  same  size  of  aperture  was  adopted 
for  the  larger  instruments  during  the  partial  phases,  the  entire  aperture,  in  all  cases, 
of  course,  being  used  during  totality. 

There  being  no  place  in  the  city  where  the  larger  instruments  could,  with  con- 
venience, be  set  up,  adjusted,  and  practiced  with  by  the  party  who  were  to  use  them, 
I  applied  to  Mr.  John  Sellers  for  permission  to  use  a  very  conveniently  located  portion 
of  his  grounds  in  West  Philadelphia,  and  having  prepared  a  design  for  a  temporary 
building  (with  roof,  in  part,  removable  by  sliding),  caused  it  to  be  erected,  and  had 
the  large  instruments  set  up  in  it. 

Matters  being  thus  far  advanced,  Prof.  A.  M.  Mayer,  Ph.  D.,  of  the  Lehigh  Uni- 
versity, Bethlehem,  Pa.,  who  had  agreed  to  join  our  party,  came  down  to  the  city  and 
spent  some  days  here,  during  which  the  telescopes  were  adjusted  by  him,  in  a  very 
perfect  manner,  by  a  rapid  and  convenient  method,  which  has  been  made  the  subject 
of  a  full  discussion  by  him,  as  will  be  seen  in  his  own  report  appended  hereto. 

A  number  of  experiments  were  made  by  Mr.  Willard,  at  this  time,  in  photograph- 
ing the  moon,  which  were  of  great  value  in  settling  the  time  of  exposure  which  would 
probably  be  required  in  the  total  phase. 

He  found  that  a  good  impression  could  be  obtained  of  the  full  moon  in  about  one 
minute,  and  that  an  abundantly  strong  one  could  be  secured  with  an  exposure  of  three 
minutes.  From  this  and  the  deductions  of  De  la  Rue,  that  the  light  of  the  promi- 
nences was  1 80  times  as  great  as  that  of  the  full  moon,  it  appeared  that  an  exposure 
of  from  \  of  a  second  to  1  second,  during  totality,  would  have  been  sufficient  to  secure 
images  of  these  bodies.  For  the  corona,  of  course  a  much  longer  exposure  would  be 
required,  but  no  estimate  could  be  made  as  to  what  would  be  its  duration. 

In  connection  with  these  experiments,  it  is  but  just  that  I  should  call  attention  to 
the  unwearied  patience  and  enthusiastic  energy  with  which  Mr.  Willard  devoted  him- 
self to  the  prosecution  of  this  preliminary  work.  Day  and  night,  whenever  any 
observations  were  to  be  made,  or  any  experiments  tried,  he  was  on  the  ground,  and 
on  certain  occasions  displayed  an  energy  and  determination,  combined  with  sound 
judgment,  seldom  to  be  encountered.  Thus,  it  becoming  desirable  to  shift  the  position 
of  the  building  in  which  the  telescopes  were  placed,  he  arranged  and  accomplished  this 
in  a  most  successful  manner,  though  the  operation  was  considered,  by  the  professional 
builders  present,  impossible  without  derangement  of  the  instruments. 

Mr  0.  H.  Kendall  also  rendered  invaluable  services  in  connection  with  the  pre- 
liminary arrangements. 


120  ECLIPSE  OF  T1IK  SUN,  AUGUST  7,   ISli'.i. 

Much  interruption  was  experienced  from  bad  weather  after  this,  but  the  rainy 
days  were  utilized  by  Mr.  Zentmayer  in  putting  the  driving1  clocks  of  both  instruments 
(which  were  in  very  bad  order)  in  admirable  adjustment,  so  that,  on  the  few  occasions 
that  the  sun  did  shine,  enough  work  was  done  by  the  rest  of  the  party  to  make  them 
familiar  with  the  necessary  manipulations. 

The  instruments  were  dismounted,  boxed,  and  packed  in  the  special  car  furnished 
us  by  Colonel  Scott,  on  Saturday,  July  31,  when  it  was  found  that,  with  the  various 
photographic  appliances,  they  made  no  less  than  five  furniture  cart  loads  of  material. 

On  Monday,  August  2,  we  started,  and  on  Wednesday,  the  4th,  about  noon, 
reached  Burlington,  Iowa,  on  the  bank  of  the  Mississippi. 

In  arranging  the  division  of  our  party  into  three  sections,  with  the  three  tele- 
scopes, so  that  they  might  be  distributed  along  the  line  of  totality,  and  thus  diminish 
the  chance  of  universal  extinction  by  local  clouds,  I  was  chiefly  guided  by  the  desire 
of  securing  in  each  section  such  a  diversity  of  special  ability  as  might  make  each  self- 
dependent  and  complete  ;  also,  to  leave  nothing  undone  to  secure  content  and  harmony 
of  feeling.  I  assigned  myself  to  the  University  telescope,  which,  being  of  smaller  size, 
and  without  clock-work  movement,  coul,d  not  be  expected  to  do  as  good  work  as  the 
others;  though,  should  they  by  chance  be  overclouded,  its  result  would  be  invaluable. 

I  therefore  divided  the  party  as  follows : 

With  the  High  School  telescope,  6-inch  aperture,  9  feet  focal  length,  Prof.  A.  M. 
Mayer,  Ph.  D.,  and  Mr.  O.  H.  Kendall  in  charge  of  the  adjustment  of  the  instrument 
and  management  of  the  apparatus  for  exposures,  and  Messrs.  O.  H.  Willard,  H.  C. 
Phillips,  and  J.  Mahoney  having  charge  of  the  entire  photographic  work.  This  sec- 
tion was  stationed  at  Burlington,  40°  48'  20"  N.,  o1'  56™  13"  West  of  Washington. 

With  the  Gettysburg  telescope,  6-inch  aperture,  8£  feet  focal  length,  Prof.  C.  F. 
Himes,  Mr.  J.  Zentmayer,  and  Mr.  E.  Moelling,  in  charge  of  the  instrument,  &c.,  and  Mr. 
J.  C.  Browne  and  Mr.  W.  J.  Baker,  who  managed  all  the  photographic  processes.  This 
party  was  stationed  at  Ottumwa,  about  seventy-five  miles  nearly  west  of  Burlington. 

With  the  University  telescopes  were  Mr.  E.  L.  Wilson,  and  myself,  in  charge  of 
the  instrument,  and  Messrs.  H.  W.  Clifford,  James  Cremer,  and  W.  V.  Ranger,  as  pho- 
tographers. We  were  also  joined  by  Mr.  John  Corbutt,  of  Chicago,  as  a  volunteer, 
who  gave  us  most  efficient  aid.  This  section  was  placed  at  Mount  Pleasant,  between 
the  other  stations.  The  various  parties  having  reached  their  destinations  during  Wed- 
nesday, arrangements  were  at  once  made  to  get  the  instruments  into  position  in  the 
locations  previously  prepared  by  Professor  Coffin.  In  the  case  of  the  Burlington 
party,  all  went  smoothly,  and  the  dark  weather  alone  prevented  final  adjustment  until 
the  night  of  the  6th  or  morning  of  the  7th,  when  this  was  secured  with  great  nicety 
by  Professor  Mayer,  who  sat  up  all  night  for  the  purpose. 

With  the  Ottumwa  instrument  it  was,  however,  found  that  the  clockwork  had 
become  seriously  deranged  in  carriage,  so  that  Mr.  Zentmayer  was  obliged  to  take  it 
entirely  apart  and  refit  it.  This  he  accomplished  with  great. success,  and  it  may  be 
regarded  as  one  of  our  many  pieces  of  providential  good  fortune,  that  since  one  of 
the  clocks  was  to  go  wrong  on  the  journey,  it  was  that  one  which  was  within  reach  of 
this  gentleman's  skill.  The  trouble  and  anxiety  which  this  cause  of  delay  occasioned, 


REPOKT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 

was,  however,  no  small  trial  of  fortitude  to  the  Ottumwa  party.  The  final  adjustment 
was  also  given  to  this  instrument  during  the  morning  of  the  7th,  by  Mr.  Zentmayer, 
who  had  watched  all  night,  vainly,  for  a  star. 

This  party,  beside  the  above-mentioned  difficulties,  were  unable  to  obtain  any  ex- 
pert assistance  on  the  ground,  from  resident  photographers  and  others,  as  was  done  by 
both  the  other  divisions,  so  that  they  were  left  entirely  to  their  own  resources,  and 
acquitted  themselves,  under  the  exceptional  difficulties  of  their  position,  in  a  most 
creditable  manner. 

In  this  connection,  special  reference  should  be  made  to  Prof.  C.  F.  Himes,  who, 
by  his  skill,  judgment,  and  coolness  in  a  serious  emergency  (occasioned  by  accidental 
derangement  of  the  chronograph  attached  to  the  telescope),  preserved  the  record  of 
this  series  of  pictures  which  must  otherwise  have  been  in  great  part  lost. 

The  telescope  at  Mount  Pleasant  having  no  clockwork,  and  being  otherwise  unfit 
for  any  fine  adjustment,  required  no  arrangement,  except  what  could  be  given  during 
the  morning  of  the  7th. 

As  all  know,  the  weather  on  the  eventful  day  of  the  eclipse  was,  at  all  our 
stations,  perfect,  so  rendering  needless,  but  none  the  less  judicious,  our  policy  of 
distribution. 

At  the.  Burlington  station,  a  photographic  record  of  the  first  contact  was  secured, 
by  exposing  plates,  in  rapid  succession,  about  the  calculated  time.  A  very  good  result 
was  thus  obtained. 

At  Mount  Pleasant,  we  placed  a  plate  ready  in  the  camera,  and  then  waited  a 
signal  from  Professor  Watson,  of  the  University  of  Michigan,  who,  with  his  party, 
was  on  the  ground  with  us,  and  was  watching  for  the  first  contact.  We  thus  obtained 
a  picture  showing  a  very  slight  indentation.  By  measurement  of  this,  the  time  of  actual 
first  contact  can  be  reached  by  calculation,  yet  more  precisely  than  would  be  possible 
with  any  eye  observation. 

During  the  partial  phases,  accurately  timed  exposures  were  made  by  all  parties, 
at  intervals  varying  from  a  few  seconds  to  ten  minutes. 

PARTIAL    PHASE    PICTURES.* 

These  pictures  are  chiefly  of  interest  in  a  photographic  point  of  view,  as  showing 
the  accurate  adjustment  of  the  several  instruments,  and  the  excellent  condition  of  the 
photographic  material  as  well  as  the  precision  of  the  various  manipulations. 

The  serrated  character  of  the  moon's  edge  is  clearly  manifest,  and  the  same  promi- 
nent peak  or  ridge  may  be  readily  identified  throughout  an  entire  series  of  pictures. 

In  the  negative,  taken  immediately  after  first  contact  at  Burlington,  a  prominent 
mountain,  producing  a  notch  in  the  solar  edges  is  perhaps  the  most  conspicuous 
indication  of  the  contact. 

I  have  selected  an  enlargement  from  negative  No.  21,  taken  at  Burlington,  as  a 
specimen  of  this  partial  phase  pictures,  because  it  combines  most  satisfactorily  several 
features  of  interest.  It  is  given  in  Plate  IX. 

The  serrated  lunar  edge,  the  well-defined  sun  spot  with  its  border  of  faculse,  and 

*  This  article  supplied  in  Jauuary,  1871. — C. 
16  E   S 


122  ECLIPSE  OF  THE  SUN,  AUGUST  7,  ISfii). 

the  irregular  masses  of  faculons  matter  at  other  points,  and  the  strange  light  band  or 
glow  adjoining  the  lunar  edge,  are  remarkably  distinct. 

As  regards  the  cause  of  this  last-mentioned  phenomenon,  a  careful  inspection  of 
the  original  negatives  convinced  me  at  once  (as  stated  in  a  rough  draft  of  this  report 
published  in  the  Journal  of  the  Franklin  Institute  for  September,  1869)  that  it  was 
"a  question  of  deposited  silver  and  not  contrast  of  light  and  shade." 

A  similar  phenomenon  was  noticed  by  Prof.  Stephen  Alexander  in  1831  and  1860, 
and  also  by  Mr.  De  la  Rue  in  his  pictures  of  the  latter  date.  Professor  Alexander  and 
Professor  Challis*  considered  this  as  evidence  of  a  lunar  atmosphere.  Mr.  De  la  Rue, 
and  the  Astronomer  Royal  of  England,  Mr.  Airy,  however,  agreed  in  ranking  this  as 
a  peculiar  effect  of  contrast,  and  Mr.  Airy  had  shown  f  that  no  such  effect  would  be 
produced  by  a  lunar  atmosphere  if  it  were  present. 

A  repetition  of  the  experiments  suggested  by  the  Astronomer  Royal  and  Mr.  De 
la  Rue  to  prove  the  subjective  nature  of  the  phenomenon  failed  to  produce  the  effect 
described  by  them,  in  a  satisfactory  manner,  thus  proving  that  the  subjective  theory 
was  insufficient  to  explain  the  entire  phenomenon  as  exhibited  in  tlicsc.  pictures. 

I  have,  therefore,  made  the  following  experiments,  which  I  believe  will  aid  in 
throwing  light  upon  this  obscure  subject. 

I  converted  an  enlarged  print  from  one  of  the  solar  pictures  taken  soon  after  first 
contact  into  a  crescent  by  pasting  partly  over  it  a  circular  piece  of  dark  paper  taken 
from  the  background  of  another  print.  This  exhibited  a  very  faint  band  of  light, 
such  as  might  be  expected  to  result  from  contrast  with  the  sharply  denned  dark  edge, 
but  which  in  no  way  approached  in  intensity  or  extent  the  bright  line  found  on  the 
prints  of  the  actual  eclipse  negatives. 

I  then  had  this  artificial  eclipse-picture  photographed  (through  the  kindness  of 
Mr.  James  Cramer,  one  of  the  members  of  our  party,)  when  negatives  were  produced, 
showing  a  dense  deposit  along  the  lunar  edge,  and  giving  prints  which  showed  a 
"bright  line"  in  the  same  place  fully  equal,  and  in  some  cases  even  superior,  in  intensity 
to  that  produced  by  the  eclipse  negatives. 

From  this  it  would  appear  that  the  cause  of  the  bright  line  was  to  be  sought,  not 
in  the  heavens,  but  in  the  camera  or  photographic  manipulations. 

The  explanation  which  at  first  suggested  itself,  and  was  published  by  me  at  the 
time,  was  the  following : 

It  is  well  known  that  the  development  of  a  negative  depends  upon  the  presence 
of  free  nitrate  of  silver  in  the  film,  and  that  a  great  strengthening  or  intensifying  may 
be  produced  by  re-immersion  in  the  silver  bath,  and  a  repeated  application  of  the 
developer.  In  the  case  before  us,  that  part  of  the  plate  representing  the  dark  disk  of 
the  moon,  and  therefore  not  acted  upon,  furnishes  a  reservoir  of  nitrate  of  silver, 
imbibed  by  the  film  which,  during  the  development,  penetrates  for  a  short  distance 
into  the  portion  representing  the  luminous  surface  of  the  sun,  whose  supply  of  free 
nitrate  was  exhausted  by  the  reaction  which  occurred  on  the  first  application  of  the 
developer.  A  similar  action  no  doubt  occurs  on  the  outer  margin  of  the  sun,  but  it 
can  there  only  diminish  the  graduated  shade  which  we  know  to  exist  in  that  part. 

*  Monthly   notices  of  the  Royal  Astronomical  Society,  1863,  p.  234. 

t  Monthly  notices  of  the  Royal  Astronomical  Society,  1863,  November  13,  and  1864,  June  10. 


KEPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.          123 

A  number  of  ingenious  experiments  made  by  Dr.  Edward  Curtis,  of  New  York, 
and  which  he  has  communicated  to  me,  have  drawn  my  attention  to  other  points,  and 
have  led  me  to  make  further  trials,  which  in  conjunction  with  his  results  have  convinced 
ine  that  the  r/ututtittj  of  tree  nitrate  of  silver  in  connection  with  the  sfre>if/th  of  the 
actinic  action  to  which  the  film  was  exposed,  and  lastly  the  drainage  of  the  plate 
during  exposure,  exerted  very  important  modifying  influences  in  the  production  or 
non-appearance  of  the  "bright  line."  Thus  suppose  that  in  a  given  case  the  actinic 
impression  was  so  faint  as  compared  with  the  amount  of  free  nitrate  present  that  there 
is  a  large  excess  of  the  latter  everywhere  present  at  the  end  of  the  exposure,  no  line 
will  be  developed.  If,  on  the  other  hand,  during  the  exposure  the  actinic  influence 
is  sufficiently  strong  to  exhaust  the  capacity  for  impression  .in  any  part  of  the 
plate,  then  the  drainage  over  this  part  of  free  nitrate  will  tend  to  develop  an  increased 
deposit  in  such  parts  as  it  reaches,  or  an  infiltration  in  a  lateral  direction  may  have 
a  like  effect.  I  have  thus  observed  in  several  cases  a  marked  increase  of  the  bright 
lines  in  a  vertical  direction  as  regards  the  position  of  the  plate  when  in  the  camera. 

As  regards  the  absence  of  the  bright  line,  I  have  found  it  invariably  wanting  when 
a  short  exposure  was  made  on  a  plate  fresh  from  the  bath,  and  Dr.  Curtis  has  obtained 
on  the  same  stereoscopic  plate  one  image  of  an  object  with  the  "bright  band,"  and 
another  without  the  exposures  being  simultaneous,  but  the  lens  which  gave  no  band 
being  reduced  in  aperture. 

I  would  then  conclude  that  the  phenomenon  of  the  "bright  band"  so  conspicu- 
ously illustrated  in  the  accompanying  impression  is  one  of  photo-chemical  origin,  and 
originates  in  the  sensitive  film  during  its  employment,  but  that  it  depends  upon  the 
co-existence  of  several  conditions  and  may  either  be  absent  or  suffer  certain  special 
modifications  as  these  vary. 

TOTALITY    PICTURES — :THE    PROMINENCES. 

During  the  totality  thirteen  pictures  in  all  were  taken  with  the  three  instruments. 
Of  these  six  were  made  at  Burlington,  with  exposures  of  five  to  seven  seconds;  four 
were  made  at  Ottumwa,  with  times  of  exposure  ranging  from  six  seconds  to  sixteen.* 

These  are  all  admirable  negatives,  which  show  abundant  detail,  and,  in  some 
cases,  much  of  the  corona.  Three  pictures  in  totality  were  also  made  at  Mount  Pleasant, 
but,  for  want  of  a  clock-movement,  are  of  little  value.  One  of  the  Ottumwa  pictures, 
exposed  at  the  very  last  instant  before  totality,  gives  a  photographic  record  of  the 
curioiis  phenomenon  known  as  Bailly's  beads,  being  simply  the  last  glimpse  of  the 
sun's  edge  cut  by  the  peaks  of  lunar  mountains  into  irregular  spots. 

One  of  the  objects  which  it  was  considered  desirable  to  secure,  if  possible,  was 
a  view  of  the  "corona.  It  was  with  this  intent  that  some  of  the  exposures  were  made 
so  long. 

Examination  of  the  negatives  shows  us  that  five  seconds  was  more  than  sufficient 
to  secure  all  the  details  of  the  protuberances,  although  it  gave  no  decided  indication 
of  the  corona. 

The   development  proceeded  slowly  in  all  but  a  few  spots  where  very  massive 

'Two  of  the  Burlington  and  three  of  the  Ottumwa  pictures  are  given  it.  Plates  IV  to  VIII. — C. 


[24  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

prominences  were  located,  and  thus  it  was  not  thought,  at  the  moment,  judicious  to 
try  shorter  exposures;  but,  in  the  light  of  our  present  experience,  we  would  judge 
that  exposures  of  even  one  or  two  seconds,  with  persistent  development,  such  as  could 
be  best  carried  out  on  albumeni/ed  plates,  would  be  of  value  to  secure  details  in  the 
rounded  and  massive  prominences  which  appear  at  some  points. 

The  most  conspicuous  prominence  (see  Plate  X,  Fig.  i)  is  that  which,  at  a  hasty 
glance,  seems  to  resemble  the  letter  X,  but,  on  more  careful  inspection,  is  perceived 
to  be  like  an  ear  of  corn.  It  consists  of  a  solid  central  mass  inclined  at  an  angle  of 
about  45°  to  the  normal  at  the  solar  surface,  and  with  three  branches  from  near  its 
end,  one  sweeping  backwards  in  a  direction  generally  parallel  to  the  solar  surface, 
another  forward,  as  concerns  the  direction  of  the  general  mass,  and  a  third  branching 
out  a  little  below  and  running  in  the  same  direction  as  this  last.  The  appearance  of 
the  main  body,  which  is  of  a  spindle  shape,  and  with  spiral  markings,  is  highly  sug- 
gestive of  a  vortical  motion  which  has  swept  these  whiffs  of  light  matter  into  their 
peculiar  positions. 

It  was  believed  by  several  observers  that  this  object  moved  rapidly  while  they 
were  watching  it;  but  as  the  same  positions  are  shown  in  the  eight  different  negatives 
(taken  at  Burlington  and  Ottumwa)  which  contain  it,  there  can  be  no  doubt  of  its  per- 
manent character. 

It  appears,  however,  beyond  doubt  that  motion,  amid  the  light  surrounding  the 
sun,  was  observed,  as  there  is  much  accordant  testimony  on  the  subject.  But  this 
motion,  as  we  shall  presently  see,  there  is  every  reason  to  believe  existed  in  the 
corona,  and  not  in  the  prominences,  which,  however,  might  easily  have  the  appear- 
ance of  movement,  if  seen  against  a  background  of  shifting  light.  To  this  subject 
we  shall  refer  again  when  speaking  of  the  corona. 

Immediately  to  the  right  of  this  ear  of  corn  is  seen  a  region  of  soft  light,  among 
which  rise  two  similar  spindle-shaped  masses  inclining  toward  the  corn  ear. 

To  the  left  appears  a  mass  of  rolling  cloud  disposed  in  beautiful  streams  and 
curls,  like  the  smoke  from  a  bonfire  or  burning  meadow,  swept  gently  toward  one 
side  by  a  light  wind.  In  connection  with  these  are  some  small  masses,  entirely 
detached  and  floating  above  the  general  body,  as  was  the  case  in  De  la  Rue's  pictures. 

Other  solid  nodular  masses  appear  at  other  points ;  but  the  next  most  notable 
prominence  is  one  which  attracted  the  attention  of  all  observers,  and  appeared  to 
occupy  a  position  on  the  lowermost  edge  of  the  sun.  It  is  most  clearly  shown  in  the 
last  totality  pictures  taken  at  each  station,  and  resembles  in  shape  a  great  whale  with 
a  body  made  up  of  dense  cumulous  cloud  matter,  with  a  long  tail  clinging  close  to  the 
solar  edge,  and  stretching  some  40,000  miles  along.  The  length  of  the  entire  mass  is 
about  110,000  miles,  and  the  height  of  its  more  bulky  portion  about  28,000  miles, 
while  its  length  is  about  70,000  miles. 

To  the  right  of  this,  and  only  showing  its  entire  length  in  the  last  picture  of  each 
series,  is  a  caterpillar-like  mass  of  cloud  matter,  very  much  like  the  solid  rolls  of  hori- 
zontal vapor  which  are  sometimes  seen  passing  over  a  sheet  of  water.  At  one  end 
rises  a  projecting  head,  but  the  rest  clings  closely  to  the  solar  edge,  and  is  indented 
with  ring-like  divisions,  giving  it  much  the  aspect  of  a  huge  worm. 


KEPOKT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.  125 

THE   CORONA.* 

[Universal  experience  has  shown  that  the  actinic  power  of  the  coronal  light  ]is 
extremely  feeble,  and  the  successful  photographic  record  of  its  detail  and  extent  would 
therefore  have  been  inconsistent  with  securing  any  valuable  representation  of  the 
prominences.  In  fact,  the  best  or  most  extensive  photograph  of  the  corona  obtained 
during  this  eclipse  was  a  picture  taken  by  the  Messrs.  Houver,  photographers  at  Mount 
Pleasant,  at  the  suggestion  of  Professor  Pickering,  with  a  globe  lens  of  1 2  inches 
focal  length.  The  camera  was  previously  pointed-  toward  the  sun  and  the  plate 
exposed  during  the  entire  totality.  The  accompanying  wood  cut  gives  a  fair  repre- 
sentation of  the  negative  obtained  enlarged  two  diameters,  and  shows  the  marked 
predominance  of  rays  in  the  direction  of  the  sun's  equator  and  axis. 

The  following  cut  represents  the  position  of  the  corona  as  it  appeared  in  the  sky 
at  Mount  Pleasant,  the  edges  of  the  black  ground  being  vertical  and  parallel  with 
the  horizon  respectively.] 


The  Ottumwa  pictures,  of  long  exposure,  give  us  some  idea  of  the  true  structure 
of  the  corona.  One  of  them  (Plate  VIII),  the  last  and  longest  exposed,  gives  the 
curved  structure  of  the  rays,  and  the  varying  intensity  with  which  they  are  emitted 
in  different  points  is  most  marked. 

The  brightest  outbursts  of  the  corona  light  are  evidently  associated  with  those 
prominences  which  are  of  a  pointed  and  flame-like  shape;  those  of  a  massive  descrip- 
tion, on  the  contrary,  seeming  to  cast  a  shadow  on  the  corona;  this,  we  think,  is  to  be 
noticed  in  De  la  Rue's  pictures. 

These  facts  have  peculiar  significance,  when  taken  in  connection  with  others 
developed  by  observations  made  during  this  same  eclipse  In  the  first  place,  Prof.  E. 
C.  Pickering,  of  the  Massachusetts  Institute  of  Technology,  who  was  with  our  party  at 
Mount  Pleasant  for  the  purpose  of  making  various  physical  observations,  found  that 
while  the  sky  was  strongly  polarized  all  around,  close  up  to  the  corona,  that  object 
itself  was  not  a  source  of  polarized  light. 

The  instrument  employed  was  a  tube,  having  at  one  end  a  large  plate  of  quartz, 
and  at  the  other  a  double  image  prism  of  Iceland  spar,  made  in  the  manner  known  as 
the  prism  of  Rochon. 

On  looking  through  this  at  the  corona,  the  entire  circle  was  in  field  with  a  part  of 
the  surrounding  sky,  and  two  entirely  distinct  images  of  the  entire  area  were  seen,  the 
corona  in  both  being  colorless,  but  projected  on  a  ground  of  tints,  complementary  in 
the  two  images. 

*  The  portion  of  this  article  in  [brackets]  was  supplied  in  January,  1871.  See  in  connection  with  it  Professor 
Pickering's  article  on  "Photographing  the  Corona,"  in  Journal  of  the  Franklin  Institute,  LX1I,  p.  54,  and  given 
hereafter. — C. 


126  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

This  would  certainly  indicate  that  the  light  of  the  corona  was  not  reflected  sun- 
light. With  a  spectroscope  arranged  to  analyze  the  entire  light  from  the  totality  phase, 
Professor  Pickering  also  found  no  dark  lines  in  the  spectrum.  This  also  points  in 
the  same  direction. 

The  observations  of  Prof  C.  A.  Young,  of  Dartmouth  College,  Hanover,  N.  H., 
who  was  stationed  at  Burlington,  are  most  conclusive.  He  found  bright  lines  in  the 
spectrum  of  the  corona  corresponding  with  those  given  by  the  aurora.  In  a  letter 
which  I  have  just  received  from  him,  he  says: 

ince  returning,  I  have  seen  the  July  No.  of  Silliman,  and  in  it  the  positions 
given  by  Winlock  for  5  aurora  borealis  lines.*  You  will  be  interested  to  learn 
that,  so  tar  as  I  can  ascertain  by  graphical  construction,  the  aurora  line  at  1550  of 
Huggins'  chart  exactly  coincides  with  my  principal  corona  line  1474  Kirchhoff;  and, 
moreover,  the  aurora  lines  1280  and  1400  (Huggins)  agree,  as  far  as  I  can  judge, 
with  the  two  fainter  corona  lines  between  D  and  K,  which  I  saw  and  recorded,  but  had 
not  time  to  measure  accurately. 

"Perhaps  I  am  too  bold  in  my  conclusions,  but  at  present  I  feel  persuaded  that 
the  solar  corona  is  a  permanent  aurora." 

It  would  thus  seem  almost  certain  that  the  corona  is  simply  an  electric  discharge, 
no  doubt  varying  with  great  rapidity,  as  we  see  in  the  case  of  the  aurora,  and  to  its 
variations  we  may  attribute  those  apparent  motions  of  the  prominences  which  have 
been  observed  by  so  many,  but  which  our  large  series  of  photographs  so  conclusively 
shows  not  to  have  had  any  actual  existence.! 

Before  closing  this  report,  I  cannot  refrain  from  saying  a  few  words  in  reference 
to  the  members  of  my  party. 

Our  labor  was  eminently  a  cooperative  one,  and  the  pleasing  success  which  has 
attended  our  efforts  is  largely  due  to  the  thorough  harmony  of  effort  and  the  self- 
denial  and  devotion  to  the  general  cause,  irrespective  of  individual  interest,  which  has 
characterized  the  entire  history  of  this  expedition. 

The  work  we  had  in  hand  was  of  a  nature  which,  in  the  first  place,  required  the 
combination  of  a  high  order  of  ability  in  many  distinct  branches.  It  was  necessary 
that  the  best  optical  skill  should  be  enlisted  in  the  structure  and  arrangement  of  the 
lenses;  it  was  essential  that  the  very  best  mechanical  ability  should  be  applied  to  the 
details  of  the  various  adjustments  of  clockwork  and  cameras;  the  largest  experience 
in  photographic  operations  was  equally  necessary;  so,  also,  was  a  thorough  and  ready 
skill  hi  the  refined  details  of  practical  astronomy.  Besides  this,  it  came  of  necessity 
that  the  failure  of  any  one  would  ruin  the  work  of  all,  as  each  step  must  be  secure, 
or  the  pinnacle  of  success  could  not  possibly  be  reached. 

Under  these  circumstances,  when  we  say  that  we  have  no  failure  to  regret,  and 


*  Silliman' *  Journal,  Vol.  XLVI1I,  p.  123.  "We  are  indebted  to  Prof.  Winlock  for  the  following  interesting 
notices.  The  light  of  the  beautiful  Aurora  of  the  evening  of  April  15tb,  examined  with  the  spectroscope,  gave  five 
bright  lines  corresponding  in  position  to  the  following  lines  of  Mr.  Hugging'  scale.  1280  (brightest),  1400,  1550, 1680, 
near  F,  2640  near  G.  On  the  evening  of  June  6th,  the  same  lines  were  again  observed,  the  brightest  corresponding 
with  1280  of  Mr.  Huggius'  scale.  These  lines  could  readily  be  seen  and  measured  with  an  ordinary  chemical  spectro- 
scope, with  the  collimator  poiuted  directly  towards  the  heavens." 

t  Mr.  Zeutmayer  observed  some  bright  objects,  eleven  or  thirteen  in  number,  crossing  the  lunar  disk,  generally 
from  one  cusp  to  the  other.    These  were  noticed  by  other  observers  in  other  places. — C. 


KEPOKT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.         127 

that  no  reproach  lias  had  cause  to  be  uttered,  the  highest  commendation  possible  has 
been  implied  towards  all  and  every  one  concerned. 

Where  all  were  unremitting-  in  effort  and  excellent  in  execution,  it  is  not  easy,  without 
injustice  to  any,  to  indicate  the  special  merit  developed,  by  opportunity  or  trying  emer- 
gency in  some;  but  we  cannot  refrain  from  drawing  especial  attention  to  the  very 
valuable  aid  which  was  afforded  by  Professor  Mayer,  Ph.  D.,  through  his  intimate 
familiarities  with  all  the  niceties  and  most  refined  improvements  in  practical  astronomy; 
by  Mr.  Joseph  Zentmayer,  through  his  admirable  ingenuity  in  the  devising  and  con- 
struction of  the  various  mechanical  and  optical  details  required  in  the  several  instru- 
ments; by  Mr.  ().  H.  Willard,  through  the  unsparing  devotion  of  time  and  energy, 
and  the  indomitable  perseverance  by  which  all  the  preliminary  arrangements  were 
pushed  to  a  successful  issue,  and  his  own  department  developed  to  its  highest  perfec- 
tion; and  by  Prof.  C.  F.  Himes,  through  the  sound  judgment  and  presence  of  mind 
displayed  on  a  trying  and  sudden  emergency. 

While  affording  gladly  this  special  distinction  to  some,  we  repeat  that  all  were 
equally  meritorious,  and  that  the  work  of  no  one  would  have  been  of  the  least  value 
without  the  aid  of  the  others. 

I  have  also,  on  my  own  behalf,  as  well  as  on  that  of  my  colleagues,  to  thank  you 
for  that  uniform  kindness,  courtesy,  and  consideration  which  has  rendered  all  our  re- 
lations of  the  most  agreeable  character,  and  made  our  labor  of  love  in  an  equal  degree 
a  labor  also  of  pleasure. 

Very  respectfully,  yours, 

HENRY  MORTON. 
Prof.  J.  H.  C.  COFFIN, 

Superintendent  of  the  Nautical  Almanac,  WasJiint/ton,  I).  C. 


REPORT  OF  ALFRED  M.  MAYER,  PH.  .D. 

(Chief  of  the  Burlington  Section  of  the  Photographic  Expedition). 

To  Prof.  HENRY  MORTON,  PH.  I).: 

DEVR  SIR:  I  herewith  present  to  you  my  report,  as  chief  of  the  Burlington  section 
of  the  Photographic  Expedition,  organized  by  you  under  the  authority  of  Prof.  J.  H. 

C.  Coffin,  U.  S.  N.,  Superintendent  of  the  Nautical  Almanac. 
This  report  is  given  under  the  following  heads: 

1.  Diary  of  work  at  Burlington  up  to  the  time  of  the  eclipse. 

2.  The  station. 

3.  The  equatorial  and  its  adjustments  in  altitude  and  azimuth 

4.  The  camera  and  chronograph. 

(«..)  The  adjustment  of  the  reticule  of  the  camera. 

(i.)  The  experimental  determination  of  the  time  of  exposure  during 
partial  phase. 

5.  The  work  during  the  eclipse. 

6.  Description  of  the  photographs  taken. 
7    Results : 

(a.)  Time  of  first  contact. 

(J>.)  Position-angles  of  first  and  fourth  contacts. 
(c.)  Angles  of  position  and  heights  of  the  protuberances. 
(<t)  Measurements  on  the  solar  spot  in  SW  quadrant. 

8.  Observations  on  the  application  of  photography  to  the  determination  of  the 
times  of  contacts  during  the  transit  of  Venus  in  1874  and  1882. 

I.    DIARY  OF    WORK  AT  BURLINGTON  UP  TO  THE  TIME  OF  THE  ECLIPSE. 

Our  party,  consisting  of  Messrs.  O.  H.  Willard,  H.  C.  Phillips,  J.  Mahoney,  O. 
II.  Kendall,  Miles  Rock  (who  accompanied  the  expedition  as  my  special  assistant),  and 
myself,  arrived  at  Burlington,  Iowa,  about  noon  on  Wednesday,  August  4. 

We  were  here  received  by  Professor  Coffin,  who  had  previously  selected  our  station 
of  observation,  and  on  it  had  erected  a  building  to  contain  the  equatorial,  with  adjoin- 
ino-  rooms  suitable  for  photographic  purposes.  The  afternoon  was  occupied  in  the 
transportation  of  our  boxes  to  the  observatory  and  in  unpacking  and  mounting  the 
telescope,  while  Mr.  Willard  made  some  additions  to  the  photographic  rooms  and 
modifications  in  their  arrangement.  We  had  progressed  so  well  with  our  work  that 
by  sundown  we  had  put  together  the  base  and  frame  of  the  telescope,  had  mounted 
bed-plate,  polar  and  declination  axes  and  circles  and  the  cradle  which  holds  the  tel- 
escope tube. 

On  Thursday,  August  5,  the  tube  was  placed  in  the  cradle  and  all  the  parts  of 
the  telescope  were  put  together  and  oiled.  The  verniers  were  now  adjusted  opposite 
each  other,  and  the  instrument  was  brought  into  altitude  adjustment  to  within  i'  by 
the  process  described  below. 

17  E  g  129 


130  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

Mr.  Austin,  of  the  Nautical  Almanac  Office,  at  the  request  of  Professor  Coffin,  had 
previously  run  a  meridian  line  on  the  cross-timbers  which  supported  the  base  of  the 
telescope,  and,  as  near  as  could  be  determined,  I  brought  the  polar  axis  and  this  line 
into  one  plane.  This  forethought  of  Professor  Coffin  greatly  expedited  the  bringing 
of  the  equatorial  into  position,  and  I  afterwards  found  from  star  observations  that  the 
azimuth  adjustment  required  to  be  touched  but  slightly. 

We  rose  on  Friday  morning,  August  6,  to  see  a  driving  rain,  with  an  east  wind 
and  the  same  dull  murky  atmosphere  which  we  had  had  all  the  day  before.  Yet  we 
went  on  attending  to  the  details  of  arrangements  for  the  coming  day  as  though  we 
could  not  be  disappointed  after  weeks  spent  in  previous  preparation  for  the  work  of  to- 
morrow, and  after  having  come  over  a  thousand  miles  to  carry  back  with  us  the  long 
thought  of  eclipse,  fixed  on  our  plates  in  appearance,  time,  and  position. 

As  we  retired  there  appeared  a  breaking  away  in  the  clouds,  and  Dr.  Gould  told 
the  clerk  in  the  office  to  "wake  us  up  if  the  stars  came  out."  We  had  barely  lost 
ourselves  in  cloudy  slumber  when  the  clerk  knocked  at  the  door  with  "Get  up!  jtlniifi/ 
of  stars!"  We  were  soon  dressed,  and  Professor  Coffin,  Dr.  Gould,  and  I  were  up  all 
night,  putting  our  own  special  instruments  in  adjustment,  and,  at  the  same  time,  help- 
ing each  other  as  we  could.  .  When  all  was  finished  the  sun  was  rising  over  the  trees 
on  the  opposite  bank  of  the  Mississippi  and  the  air  was  as  pure  and  as  serene  as  one 
could  wish. 

On  Saturday  morning  the  chronograph  was  mounted  and  wires  were  led  to  the 
camera,  to  Prof.  C.  A.  Young's  spectroscope  and  to  the  station  of  Dr.  Gould  outside 
the  building.  The  two  threads  of  the  reticule  of  the  camera  were  placed  one  parallel 
and  the  other  at  right  angles  to  the  celestial  equator.  Mr.  Willard  now  began  experi- 
ments to  ascertain  the  chemical  focus,  and  his  success  in  this  delicate  adjustment  will 
speak  for  itself  to  all  who  examine  the  beautiful  details  of  the  photographs. 

Is  is  here  important  to  remark  that  the  chemical  focus  was  obtained  after  the  tube 
had  been  following  the  sun  for  an  hour  or  more,  and  after  the  focus  was  fixed  the 
clock-work  was  kept  going  so  that  no  change  in  focus  should  supervene  from  a  change 
in  temperature  in  the  lenses  and  tube,  which  change  of  focus  certainly  would  have 
occurred  if  we  had  closed  the  roof  of  the  observatoiy  and  had  uncovered  only  a  short 
time  before  the  eclipse. 

By  3  p.  m.  all  was  in  readiness  and  each  one  at  his  allotted  post  of  duty  ready 
for  work.  We  were  now  surrounded  by  a  clear,  soft  atmosphere  without  the  slightest 
haze,  and  no  trace  of  clouds  except  a  small  low  bank  on  the  western  horizon.  The 
temperature  of  the  air  was  71°  Fahr. 

2.    THE    STATION. 

The  station  selected  for  us  by  Professor  Coffin  was  situate  on  an  eminence  known 
as  South  Hill,  in  the  southwest  part  of  the  town  of  Burlington.  The  inclosure  was  ;i 
level  square  of  ground  thickly  covered  with  clover  grass  and  surrounded  by  a  hedge. 
It  was  elevated  about  175  feet  above  the  river,  and  its  quiet  and  freedom  from  dust 
rendered  it  admirably  suited  to  our  purposes. 

The  latitude  of  our  station  in  .Burlington  is  40°  48'  20"  N.  Longitude,  o1' 
56m  I38.8  W  of  Washington.  It  was  about  7  miles  north  of  the  center  of  the  moon's 
shadow. 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.  131 

3.      THE    EQUATORIAL    AND    ITS    ADJUSTMENTS. 

The  equatorial  was  borrowed  from  the  observatory  of  the  Central  High  School 
of  Philadelphia,  and  is  by  Merz  and  Mahler,  of  Munich.  It  is  of  9  feet  focus  and  6.42 
inches  aperture,  and  was  mounted  on  one  of  Fraunhofer's  wooden  stands.  It  has  a 
driving  clock,  the  movement  of  which  is  governed  by  the  friction  of  revolving  arms 
against  the  inner  surface  of  a  cone,  and  by  bringing  the  knobs  (which  terminate  the 
arms  and  are  attached  to  them  by  springs)  to  run  against  a  larger  or  smaller  circum- 
ference of  the  cone  we  obtain  a  greater  or  less  velocity  of  clock-movement. 

The  stand  of  the  telescope  rested  on  massive  cross-timbers  firmly  rammed  in  the 
ground. 

The  object-glass  of  this  instrument  had  a  light  brownish  tinge,  which  it  is  im- 
portant to  remember,  as  it  may  have  had  some  effect  on  the  chemical  action  at  its 
focus. 

The  probability  of  cloudy  weather  immediately  preceding  the  eclipse  caused  me 
to  use  the  following  method  of  adjustment ;  and  it  is  well  I  did,  for  otherwise  I  should 
not  have  been  able,  in  the  few  hours  when  the  stars  did  appear,  to  have  brought 
my  telescope  into  the  exact  position  I  did. 

I  had  the  cap,  which  covers  the  object-glass,  centered  on  a  lathe  and  pierced  with 
a  hole.  The  object-glass  and  eye-lenses  were  removed  and  a  plumb-line  was  let  fall 
from  the  hole  in  the  center  of  the  cap  through  the  hole  of  the  cap  of  the  ocular. 
When  the  line  was  brought  to  the  center  of  the  hole  of  the  eye-cap,  the  axis  of  the 
telescope  was  vertical.  The  vernier  was  now  read,  the  tube  brought  to  a  vertical  posi- 
tion on  the  other  side  of  the  polar  axis,  and  the  vernier  read  again.  The  difference  of 
readings  gives  twice  the  angle  formed  by  the  vertical  with  the  polar  axis,  and,  if  the 
polar  axis  is  elevated  to  the  latitude  of  the  place,  will  equal  twice  the  co-latitude  of  the 
station.  If  the  angle  obtained  is  too  great,  close  it  by  elevating  the  polar  axis;  if  too 
little,  open  it  by  depressing  the  axis. 

I  thus,  assisted  by  Mr.  Rock,  adjusted  the  telescope  to  within  i'.  The  error  read 
was  30".  I  say  within  i',  for  i'  on  a  radius  of  9  feet  is  .03132  inch,  and  a  deflection 
of  the  line  ,00  of  an  inch  from  the  center  of  the  ocular  cap  will  give  a  deviation  from 
centrality  of  twice  that  quantity,  or  ^  (about  ^  inch) ;  for  we  measure  with  the  eye 
from  the  sides  of  the  hole  to  the  line  and  not  from  its  center  to  the  line,  so  the  differ- 
ence of  these  measures  is  twice  the  deviation. 

As  stated  above,  the  polar  axis  was  brought  as  near  as  could  be  in  one  plane  with 
the  meridian  line  previously  traced,  and  the  azimuth  adjustment,  tested  in  the  following 
manner,  required  only  a  slight  alteration. 

To  bring  polar  axis  into  the  plane  of  the  meridian. — Select  an  equatorial  star  and 
place  micrometer  thread  so  that  the  star  glides  along  the  thread  when  the  telescope  is 
moved  in  right  ascension.  The  thread  is  now  nearly  parallel  to  the  equator.  Select 
a  star  about  three  hours  off  the  meridian,  say  W ,  and  bring  it  on  equatorial  thread  of 
micrometer  and  set  the  clock  going.  If  the  star  (as  seen  in  a  refractor  with  a  direct 
eye-piece)  rises  above  the  thread,  then  N.  end  of  polar  axis,  is  E.  of  the  meridian;  if 
the  star  falls  below  the  thread,  then  N.  end  of  axis  is  W.  of  meridian  plane.  If  an 
E.  star  is  used,  then  the  above  rule  is  reversed  (E.  for  W.,  &c.) 


132  ECLIPSE  OP  THE  SUN,  AUGUST  7,  1809. 

After  each  adjustment  the  equatorial  wire  is  reset  to  the  equator,  and  the  opera- 
tions are  continued  until  the  star  neither  rises  nor  falls. 

On  the  night  of  the  6th~7th  this  adjustment  was  effected  and  the  clock,  after 
much  trouble,  regulated  until  it  drove  the  tube  so  that  a  star  was  closely  bisected  for 
about  twenty  minutes.  During  the  adjustment  of  the  clock  the  precaution  was  taken 
to  place  the  tube  to  about  the  same  elevation  it  would  have  the  next  day  during  totality. 

4.    THE    CAMERA    AND    CHRONOGRAPH. 

The  image  of  the  sun  was  formed  on  the  plate  of  the  camera  by  the  action  of  a 
negative  eye-piece,  the  lenses  of  which  were  so  placed  by  Mr.  Zentmayer  in  relation 
to  the  object-glass  and  to  each  other,  that  the  diameter  of  the  sun's  image,  on  a  4^  by 
$%  inch  plate,  was  2.04  inches.  This  image  was  therefore  not  the  direct  image  formed 
by  the  object-glass,  but,  according  to  De  la  Rue's  plan,  adopted  and  judiciously  mod- 
ified by  you,  it  was  the  magnified  image  of  the  direct  image  which  was  used. 

(a)  The  adjustment  of  the  reticule  of  the  camera. 

Mr.  Zentmayer  had  so  constructed  the  camera  eye-piece  that  the  image  of  a 
reticule  of  two  spider  threads,  at  right  angles  to  each  other,  was  formed  on  the  plate 
with  the  image  of  the  sun,  and  these  threads  were  so  mounted  that  they  could  be 
adjusted  respectively  parallel  and  at  right  angles  to  the  celestial  equator,  and  thus  fix 
on  the  photographs  the  positions  of  the  sun  and  moon,  and  give  the  position-angles 
of  points  on  the  surface  and  periphery  of  the  sun.  This  adjustment  I  deemed  of 
great  importance,  as  without  it  we  would  not  obtain  the  position-angles  of  contact  nor 
the  positions  of  the  protuberances  during  totality.  The  lines  are  nearly  as  sharply 
defined  on  the  pictures  of  totality  as  on  those  taken  during  partial  phase. 

The  adjustment  was  made  as  follows :  The  camera  was  firmly  screwed  to  the  tel- 
escope and  the  focussing  tube  was  moved  until  the  images  of  the  sun  and  threads  of 
the  reticule  w.ere  brought  to  exact  focus  on  the  ground  plate.  The  well-defined  spot 
in  the  SW.  quadrant  of  the  sun  was  now  made  to  travel  along  the  thread,  by  clamp- 
ing the  telescope  in  right  ascension,  and  the  reticule  plate  revolved  until  the  spot  was 
accurately  bisected  during  all  its  progress  across  the  field.  The  telescope  was  then 
undamped  in  right  ascension  (still  remaining  clamped  in  declination),  and  moved 
around  the  polar  axis  so  that  the  spot  ran  along  the  thread;  it  was  found  to  be  bisected 
throughout  all  its  transit. 

Dr.  Gould,  at  my  request,  now  examined  the  adjustment  and  pronounced  it  precise. 

(ft)  The  experimental  determination  of  the  time  of  exposure  during  partial  phase. 

The  tube  carrying  the  camera  lenses  screwed  into  a  plate,  in  which,  immediately 
in  front  of  the  anterior  lens,  was  a  guide  in  which  a  thin  plate,  having  a  horizontal 
slot  of  .0224  inch  in  width,  was  caused  to  descend  by  the  action  of  a  spring.*  Any 
integral  ray  of  the  beam  whose  rays  successively  passed  this  slot  traversed  the  plate 
only  during  the  time  it  took  the  slot  to  fall  its  own  breadth,  or  the  .0224  of  an  inch; 
and  the  determination  of  this  time — being  the  time  of  exposure— has  been  the  object 
of  an  experimental  investigation  which  is  given  below. 

During  totality  the  full  aperature  of  object-glass  was  employed  and  a  slide-plaie 

"The  construction  was  such  that  the  plate  could  lie  made  to  descend  by  the  action  of  1,  1, or  :{  springs •  only  one 
was  used  by  me  for  the  exposures  of  both  partial  phase  and  of  totality. 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 


133 


was  used  which  had  a  circular  opening,  which  allowed  the  full  beam  to  pass.  This 
plate  had  two  falls  instead  of  one,  as  was  the  case  with  the  .02 24-inch  slide  used  during 
partial  phase.  On  setting  the  plate  free  by  the  top  trigger  it  fell,  and  the  collodion 
plate  was  exposed  to  the  entire  beam;  after  the  desired  exposure  a  lower  trigger  was 
relieved  and  the  plate  made  a  second  fall,  and,  the  lens  being  covered  by  the  top  of 
the  plate,  the  exposure  ceased. 

After  my  examination  of  the  photographs,  I  realized  the  importance  of  an  accurate 
determination  of  the  time  of  exposure  during  partial  phase,  so  that  those  who  should 
hereafter  attempt  similar  work  might  have  the  full  benefit  of  our  experience.  This  I 
considered  all  the  more  important  because  our  results  are  apparently  as  perfect  as  any 
heretofore  attained,  and  therefore  the  time  which  gave  these  results  should  be  accurately 
known. 

A  reference  to  the  diagram  of  the  camera  will  render  clear  the  method  of  register- 
ing on  the  chronograph  and  also  the  process  by  which  I  determined  the  duration  of 
the  Hash  of  the  sun  which  fixed  his  image  on  our  plates 

During  the  eclipse  the  registration  on  the  chronograph  was  effected  as  follows- 


A  circuit  passed  from  the  face-plate  A  B  to  the  chronograph  through  the  trigger'K, 
and  the  spring  attached  to  the  binding  screw  L,  which  latter  was  insulated  from  the 
slide  by  being  fixed  to  the  wooden  camera  box.  On, tapping  the  trigger  K,  the  pin  p 
of  the  slide  being  relieved  of  support,  the  slide  fell,  and  the  circuit  was  broken  by  the 
spring  under  the  trigger  no  longer  touching  the  top  of  the  spring  L.  Thus  a  break 
circuit  was  obtained  at  the  instant  of  each  exposure,  which  was  duly  registered  on  the 
chronograph.  (See  diagram,  page  1 1 7.) 

The  arrangement  of  apparatus  and  circuit  for  the  determination  of  the  time  of 
exposure  was  as  follows: 

From  the  break-circuit  clock  of  my  observatory  I  led  a  wire  to  one  pole  of  a 
battery,  thence  by  the  other  pole  to  the  place  at  H;  from  this  plate  the  current  went 


134  ECLIPSE  OF  TBE  SUN,  AUGUST  7,  1869. 

through  the  trigger  K  and  spring  at  L  to  a  Morse  register;  from  the  register  by  a  wire 
which  led  back  to  the  clock,  and  thus  completed  the  circuit.  Another  short  stiff  wire, 
o  A,  was  attached  to  the  binding  screw  L,  and  reached  from  L  to  a  short  distance 
beyond  the  slot  A,  and  was  in  front  of  the  surface  of  the  face-plate  A  B,  but  so  near 
to  it  that  when  the  slide  fell  the  projecting  pin  p  would  strike  the  wire  about  one-tenth 
of  an  inch  above  its  lowest  point  of  fall.* 

Now,  suppose  the  projecting  pin  p  to  rest  on  the  trigger  K,  while  the  spring  under 
the  trigger  rests  on  the  top  of  the  steel  spring  attached  to  L,  and  that  a  paper  fillet  is 
running  through  the  Morse  register;  then  at  every  second  the  clock  will  for  an  instant 
open  the  circuit,  and  there  will  be  a  very  short  break  made  in  the  line  marked  by  the 
pen  on  the  fillet,  and  thus  the  seconds  of  time  are  stepped  off  in  space  on  the  paper 
ribbon.  Suppose,  now,  that  the  long  end  of  the  trigger  K  be  sharply  driven  by  the 
blow  of  a  hammer  against  the  face  of  the  camera ;  the  circuit  will  be  open  during  the  fall 
of  the  pin  from  the  top  of  trigger  to  the  point  where  it  strikes  the  wire  o  A  projecting 
from  L,  and  there  will  be  produced  in  the  line  on  the  fillet  a  break,  whose  length 
compared  with  the  length  of  the  second  in  which  it  occurs  will  give  the  time  required 
for  the  plate  to  fall  the  above-mentioned  distance.  It  is  evident  that  as  soon  as  the  pin 
strikes  the  wire  the  circuit  is  again  closed,  and  the  clock  breaks  the  circuit  as  before 
the  fall.  I  always  struck  the  trigger  at  about  a  half  second,  so  that  the  comparison  could 
be  readily  and  accurately  made. 

The  fall  being  accurately  measured  and  the  time  of  that  fall  known,  the  time  the 
plate  takes  to  fall  .0224  inch,  which  is  the  time  of  exposure,  can  be  accurately  computed. 

Before  giving  the  results  of  these  experiments,  I  should  remark  that  the  plate 
descends  with  an  increasing  velocity  produced  by  the  action  of  the  decreasing  force  of 
the  spring,  and  what  I  obtained  was  the  mean  velocity  of  the  plate.  Also,  the  time  it 
took  the  pen  of  the  register  t  >  leave  the  fillet  at  demagnetization  and  return  to  the  fillet 
at  magnetization  is  neglected,  and  as  I  had  no  means  of  determining  it  I  adjusted  the 
force  of  current  and  of  spring  so  that  these  motions  were  as  rapid  as.possible.  I  do  not 
think  the  time  required  for  these  motions  has  affected  the  results  appreciably,  especially 
as  the  fall  was  a  large  multiple  of  the  breadth  of  the  slot. 

The  breadth  of  the  slot  was  measured  under  the  microscope  and  the  mean  of  three 
measures  at  ends  and  middle  gave  .0224  inch. 

As  an  example  of  the  mariner  of  determining  the  time  of  exposure  from  the  above 
data,  we  will  take  the  results  of  fillet  No.  i. 

Inch. 

Length  of  second  on  fillet 83 

Length  of  break  during  the  fall  of  slide 1 05 

Fall  of  slide i  .340 

Width  of  slot  in  plate 0224 

Time  of  fall  of  slide  through  i  .34  inch,  —  ^~—  o8. 1 26. 

O 

Time  of  exposure,  =  O"-126  *  '°224-  O8.oo2 1 1. 

1-34 


•The  wire  0  A  is  represented  in  the  engraving,  bent  upward  at  its  end  A;  it  should  bo  straight, 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 


135 


Number  of  fillet. 

Length  of  Is  on 

fillet. 

Length  of  break 
on  fillet  (luring 
fall  of  plate. 

(•'all  of  plate. 

Time  of  exposure. 

huh. 

fact. 

Inch.. 

Stc. 

I 

.830 

.105 

'•34 

.  002  i  i 

2 

.765 

.090 

i-34 

.  00196 

3 

•  79° 

.0975 

i-34 

.00205 

4 

•795 

.  100 

i-34 

.00208 

5 

.840 

.  120 

'•34 

.00237 

6 

•  78s 

.095 

i-34 

.  OO2O2 

7 

•755 

.  no 

1.36 

.O023I 

8 

.860 

.  120 

1.36 

.00228 

9 
Mean  time  of  ex 

•75° 
posure 

.  100 

1.36 

.  OO2II 

.  OO2I^ 

The  greatest  departure  in  these  results  from  the  mean  is  .0002,  No.  2  being  that 
quantity  below,  and  No  5  that  amount  above  the  mean. 

The  sum  of  the  last  column  of  figures  equals  39;  their  mean  4.33;  which  shows 
that  they  are  entirely  of  an  arbitrary  value,  and  if  the  experiments  had  been  extended 
would  no  doubt  eventually  have  equaled  4.5;  we  therefore  reject  the  last  decimal 
place,  and  adopt  for  our  final  result  .002 1  of  a  second.  The  time  of  exposure  was 
therefore  almost  exactly  one  five  hundredth  of  a  second ! 

5.    THE    WORK    DURING    THE    ECLIPSE. 

As  before  stated,  by  3  p.  m.  of  August  7  all  was  in  readiness  fpr  our  work.  Mr. 
Willard  had  used  every  precaution  to  insure  success  in  the  details  of  photographic 
manipulation,  and  the  results  which  he  reached  will  show  with  what  judgment  and 
skill  he  had  organized  all  the  workings  of  this  department. 

It  was  my  duty  to  keep  the  telescope  in  adjustment  and  to  manipulate  the  apparatus 
of  exposure  and  chronographic  registration,  while  Mr.  Willard  placed  the  plate  in  the 
camera  and  gave  me  the  several  times  of  exposure  he  desired  during  totality.  Mr.  H. 
C.  Phillips  coated  the  plates  and  handed  them  to  Mr.  Montfort  (photographer  of  Burling- 
ton), who  carried  them  to  Mr.  Willard,  and  thence  after  exposure  to  Mr.  Mahoney,  who 
developed,  assisted  by  Mr.  Leisenring. 

Mr.  Miles  Rock  was  detailed  to  attend  to  the  very  important  duty  of  calling 
and  tapping  the  seconds  on  the  chronograph  fillet;  in  this  duty  he  was  relieved  by  Mr 
Bonsall,  of  Burlington.  Mr.  ( ).  H.  Kendall  called  out  the  minutes  at  each  60  second 
call  of  Mr.  Rock  and  wrote  it  on  the  fillet.  He  also  had  charge  of  the  chronograph, 
and  started  it  when  I  called  ''clock,"  while  at  the  same  signal  Mr.  Rock  began  the 
registration  of  seconds. 

I  laid  out  the  following  programme  of  work:  (i)  To  take  in  rapid  succession, 
beginning  ten  seconds  before  the  computed  time  of  first  contact,  a  series  of  five  photo- 
graphs. (2)  One  just  before  second  contact,  one  just  after  second  contact,  as  many 
as  possible  during  totality,  one  just  before  the  end  of  totality,  and  another  just  after 
the  sun  appeared.  (3)  To  take  again  a  series  in  rapid  succession  about  the  end  of 


1 36  ECLIPSE  OP  THE  SUN,  AUGUST  7,  18C9. 

the  eclipse.  (4)  During  partial  phase  to  take  a  photograph  every  four  or  five 
minutes. 

To  accomplish  this  I  placed  on  a  table  before  me  a  watch  set  to  the  face  of  the 
chronometer,  whose  indications  we  used  during  the  eclipse,  and  on  a  slip  of  paper 
pasted  to  the  table  I  wrote  in  very  black,  lead  pencil  the  computed  times  of  ist,  2d,  3d, 
and  4th  contacts,  obtained  from  Professor  Coffin.  I  thus  could  give  Mr.  Willard  due 
notice  when  the  plates  should  be  prepared. 

When  the  face  of  the  chronometer  marked  i  2h  48™,  Mr.  Rock  began  to  count  and 
register  the  times  oh  the  fillet.  Every  one  was  at  his  post,  the  lanterns  lighted,  and 
nothing  could  be  heard  but  the  count  and  the  tap  of  the  chronograph.  At  i  2''  49'"  45", 
1  took  the  first  photograph,  and  following  at  intervals  of  11,  10.*,  15.2,  and  12  seconds 
we  secured  five  perfect  negatives.  The  contact  is  first  visible  on  the  third.  We  now 
leisurely  took  photographs  at  intervals  of  about  four  minutes,  until  \ve  had  taken  twelve 
plates  in  all.  The  moon's  limb  had  now  advanced  to  about  three  minutes  of  the  time  of 
the  spot  in  the  SW.  quadrant.  Professor  Young,  of  Dartmouth  College,  who  was 
stationed  near  me,  stated  his  intention  to  signal  as  soon  as  the  umbra  was  bisected  by  the 
border  of  the  moon.  The  plate  was  prepared  and  all  was  ready.  Professor  Young 
signaled;  I  tapped  the  trigger;  he  remarked,  "You  must  have  shot  it  on  the  wing." 
The  1 3th  plate  (No.  15)  shows  the  spot,  as  nearly  cut  in  half  as  I  can  estimate  by  a 
careful  comparison  of  this  drawing  with  another  of  the  spot,  as  photographed  on  the 
preceding  Plate  — . 

About  five  minutes  before  totality  Mr.  Willard  removed  the  diaphragm  of  two 
inches  aperature,  which  was  vised  during  partial  phase,  and  exposed  the  full  aperture 
of  the  object  glass,  while  I  changed  the  slide  with  .02 24-inch  slot  for  the  one  which 
admitted  the  whole  beam  at  once  on  the  plate  of  the  camera. 

The  order  was  given  to  prepare  the  plates.  We  took  the  first  plate  at  1 3*'5 1 '"  39".  i  5 , 
or  7"  before  the  time  of  second  contact,  as  observed  by  Professor  Coffin.  I  soon  had 
the  slide  reset  for  another  exposure,  and  as  Mr.  Willard  desired  the  first  plate  of  total- 
ity to  be  exposed  five  seconds,  T  kept  on  counting  zero,  zero,  zero,  with  the  taps  of 
the  chronograph  when,  striking  the  upper  trigger  at  zero,  I  counted  i,  2,  3,  4,  5,  when 
the  lower  trigger  was  struck  and  the  plate  removed. 

Counting  the  first  plate,  taken  seven  seconds  before  second  contact,  I  took  six 
photographs  in  2™  3".  After  the  sixth  was  removed  I  looked  at  the  watch  and  saw 
50"  yet  of  total  phase.  There  was  a  delay  in  the  plate.  I  grew  impatient.  I  called 
plate!  plate!  but,  alas,  it  was  found  impossible  to  manipulate  more  than  six  plates  in 
two  minutes  and  three  seconds.  We  had  used  up  our  store  too  rapidly,  and  so  did 
not  succeed  in  getting  an  impression  just  before  the  sun  came  forth.  The  next  plate 
was  taken  29". 2  after  third  contact,  and  is  a  valuable  photograph  of  a  thin  crescent 
with  the  cusps  sharply  cut, 

As  has  already  been  explained,  under  the  head  of  camera,  at  each  fall  of  the  slide 
the  electric  circuit  was  broken,  and  a  registration  made  on  the  fillet  alongside  of  Mr. 
Rock's  second  marks  taken  from  the  chronometer,  and  it  is  evident  that  all  of  these 
registrations  are  vitiated  with  whatever  personal  equation  affected  him  at  that  time. 
This  was  not  determined. 


i;i:roi;T  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.        137 

A!M nit  fifteen  minutes  before  totality  it  became  so  cool  that  I  was  obliged  to  put 
on  my  coat.  A  minute  or  two  before  totality  the  sky  grew  ashen,  or  rather  leaden,  in 
hue,  and  as,  with  face  turned  toward  the  sun,  I  kept  the  count  from  the  chronometer 
for  the  first  exposure,  Venus  and  Mercury  came  out  shining  beautifully  on  a  ground 
of  bluish  gray.  1  thought  I  sa\v  a  Hashing,  twirling  motion  in  the  corona,  or  in  the 
last  rays  of  the  sun;  but  of  this  1  will  not  In;  positive,  for  my  attention  was  not  at  the 
time  specially  directed  to  minute  observation.  Moths  and  insects  in  profusion  passed 
between  me  and  the  sun,  while  a  Hock  of  birds  with  troubled  irregular  Hight  seemed 
seeking  cover  from  the  unnatural  gloom  which  surrounded  them.  A  low  moaning 
wind  now  sprang  up,  and  the  whole  atmosphere  seemed  filled  with  a  leaden-colored 
vapor,  and  I  experienced  an  indescribable  feeling  of  oppression  when — I  tapped  the 
trigger,  and  from  that  instant  until  the  sun  appeared  1  had  nothing  but  an  instrumental 
consciousness,  for  I  was  nothing  but  part  of  the  telescope,  and  all  my  being  was  in 
the  work  which  I  had  to  perform.  I  reset  slide,  made  circuit,  exposed,  and  so  over 
again,  until  the  six  photographs  were  taken. 

Photographs  were  now  taken  leisurely,  at  intervals  of  about  four  minutes,  until 
i4b  47"1  /)8S4,  when  the  first  of  the  series  for  the  end  of  the  eclipse  was  secured;  this 
was  followed  by  four  others  at  intervals  of  im  i6".84,  19". 26,  248.3,  and  2i".55.  Our 
work  was  finished,  and  in  a  few  seconds  the  eclipse  of  August  7,  1869,  was  of  the  past, 
but  its  history  we  had  faithfully  recorded  in  forty-one  perfect  photographs. 

Such  good  success  as  attended  our  efforts  speaks  for  the  entire  devotion  of  each 
one  to  his  allotted  duties.  Without  this  devotion  on  the  part  of  each  and  all  we  would 
have  failed,  and  the  harmony  and  efficiency  which  pervaded  our  corps  need  no  other 
witness. 

6.    DESCRIPTION    OF    THE    PHOTOGRAPHS  "TAKEN. 

We  took  forty-one  photographs  during  the  eclipse.  They  are  all  good,  but  some 
are  superior  to  the  others,  and  these  will  be  designated  as  I  proceed. 

The  plates  were  numbered  with  a  diamond  before  the  work  began,  and  the 
numbers  corresponding  to  those  on  the  plate  are  given  below,  and  opposite  them  the 
times  when  they  were  severally  taken.  These  times  were  measured  off  from  the 
chronograph  fillet,  and  correspond  to  the  face  of  the  chronometer.* 

* //lit/on,  202,  the  correction  of  which  referred  to  /urn/ mean  time  of  the  Coast  Survey  station,  was  +  I511  6™  16". 70—  9". 63 
(t—  I2b),  /  being  the  chronometer  time  in  hours  (p.  20). — C. 
18  E  S 


138 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  isti'.t. 


No.  of  plate. 

Time  when  taken. 

No. 

of  plate.                                   Time  when  taken. 

h.   ra.      s. 

h.   m.      .s. 

••) 

....     12  49  45.  25 

25 

(7  seconds  exposure)  totality.  .    13  52  31.  3 

3  :  •  • 

....     12  49  56.0 

23 

(7  seconds  exposure)  totality.  .    13   52   54.5 

4  (after  1st  contact) 

....     12  50     5.  8 

26 

(7  seconds  exposure)  totality.  .  13  53  12.  37 

5     

....       12    50    21.  I 

27 

(7  seconds  exposure)  totality.  .    13  53  42.  2 

6    

....       12    50    32.95 

28 

'3  55      1-2 

8    

•    •    •    •    12  53     5-3 

29 

'3  57  20.  5 

9    

12    56      3-2 

3° 

13  5«     5-5 

10    

•    -    •    •    12  57  33-4 

ji 

14       2    41.  0 

ii     

.    .    .    .    12  59  17.6 

32 

14     7  14-67 

12      

....       13       2    IS.  I 

33 

H  H  33-5 

'3      

-    •    •    .    13     7  23.  3 

34 

14  16  59.  6 

'4    

.    .    .    .    13  12  19.27 

35 

M  23     1.5 

«s  

....    13  15   14.24 

36 

;  .  .  ;    14  29  21.5 

16    

-     •      •     •       '3    22    57.5 

37 

14  3"  33-5 

17    

.-...'.       13    20    55.6 

38 

-    -    -    •     H  44  33-  ' 

18    .    :    

•    -    •    •     13  32  58-° 

39 

H  47  4&  4 

19    

.    ...   '13  37  4i-5 

40 

....     14  49     5-24 

20      

....     13  41  50.  6 

41 

•     14  49  24-  5 

21       

....     13  46  34.  i 

42 

just  before  end  <>f  eclipse    .    .     14  49  48.  8 

22  (5  seconds  exposure) 

totality.  .   13  51   39-  15 

43 

14  50   10.  35 

24  (5  seconds  exposure) 

totality.  .   13  52     3.  I 

All  the  photographs  show  a  beautiful  gradation  of  shade  from  the  border  of  the 
sun  inwards.  This  shading  of  the  source  of  light  is  due  to  the  absorption  of  the  periph- 
eral rays,  which  necessarily  pass  through  a  greater  thickness  of  the  dense  solar 
atmosphere  than  those  which  emanate  from  the  central  portion  of  the  disk. 

On  a  more  searching  examination  of  the  relative  intensities  of  light  of  different 
portions  of  the  solar  disk,  we  observe  on  all  of  these  photographs,  close  to  the  limb  of 
the  advancing  or  retreating  moon,  a  bright  glow  like  that  of  early  dawn,  which 
extends  from  the  moon  to  a  distance  of  about  1 5". 

Thinking  that  this  might  be  subjective  and  due  to  the  strong  contrast  existing 
between  the  bright  image  of  the  sun  and  the  contiguous  black  lunar  disk,  I  made  the 
following  experiments: 

I  covered  the  image  of  the  moon  with  a  disk  of  white  paper  of  its  exact  diameter. 
The  plate  was  now  inclined  to  the  light,  so  that  the  sun  and  the  paper  surface  had  as 
nearly  as  possible  the  same  white  tint,  while  the  photograph  was  viewed  against  an 
illuminated  ground  formed  by  a  sheet  of  white  paper  placed  before  the  window 
Under  these  circumstances  the  glow  remained  the  same  in  all  the  photographs 
examined  Among  others,  plate  No.  1 1  (which  is  the' best  photograph  of  partial  phase 
in  the  series)  shows  this  glow  unequivocally. 

Plates  Nos.  21  and  30  are  excellent  photographs  of  thin  crescents  of  the  sun;  the 
first  taken  5™  12"  before  and  the  second  3™  33".  5  after  totality.  This  glow,  if  it  really 
exist,  should  show 'in  these  pictures  an  increased  illumination  in  the  points  of  the 
cusps  when  the  light  of  these  portions  of  the  periphery  of  the  sun  is  compared  with  an 
equal  breadth  of  the  sun's  border,  taken  on  that  portion  of  its  limb  the  farthest  from 


K'KI'ORT  OF  TIIK   I'HILADKU'HIA   PHOTOGRAPHIC   KXPKDITION.          139 

the  moon's.  To  make  this  comparison  T covered  with  white  paper  both  the  moon  and 
the  dark  ground  surrounding  the  sun,  and  inclined  the  plates  as  in  the  above  experi- 
ments, so  as  to  destroy  irradiation  from  juxtaposition  of  the  light  and  dark  surfaces. 
This  method  of  examination  showed  a  distinct  illumination  in  the  narrowest  portions 
of  the  horns  of  the  crescents. 

No  such  glow  is  seen  on  the  periphery  of  the  sun,  althongh  this  is  contiguous  to 
the  dark  ground  of  the  plate,  and  on  covering  the  latter  the  appearance  remains  the 
same. 

T  am  therefore  convinced  that  this  glow  really  exists,  and  if  it  cannot  be  accounted 
for  in  mode  and  in  mnix/n-c,  by  diffraction,  it  must  be  due  to  a  lunar  atmosphere; 
though  I  confess  I  cannot  understand  how  an  atmosphere  capable  of  producing  such 
marked  effects,  when  projected  against  the  intensely  lighted  disk  of  the  sun,  should 
have  no  appreciable  refractive  effect  on  small  stars,  and  especially  on  double  stars, 
when  occulted  by  the  moon.* 

This  glow  can  be  distinctly  traced  on  plate  No.  11  to  18"  beyond  the  limb  of 
the  moon. 

A  minute  examination  of  these  photographs  reveals  a  coarsely  granulated  or 
mottled  surface  extending  over  the  sun,  and  especially  well  defined  as  we  near  its 
border.  <  )ne  is  tempted  at  first  to  imagine  that  this  is  the  well  known  solar  granula- 
lion  observed  in  the  telescope;  but  familiarity  w'th  that  appearance,  as  well  as  the 
reasons  given  below,  soon  decided  me  to  reject  the  idea  that  this  appearance  on  the 
photographs  \vas  really  an  impression  produced  by  the  image  of  the  sun's  granulation 
on  the  plate. 

First,  the  granulations  are  many  times  larger  than  any  ever  yet  observed,  those  on 
the  photographs  averaging  7". 5  in  diameter,  while  those  on  the  sun  average  i",  and 
never  exceed  3"  in  diameter;  secondly,  on  plate  No.  14  the  mottling  is  very  apparent,  and 
encloses  a  space  entirely  free  from  granulation  in  the  NE.  quadrant;  no  corresponding- 
vacant  space  occurs  in  any  of  the  other  photographs;  thirdly,  the  positions  of  these 
granulations  are  not  the  same  on  any  two  plates,  as  I  found  from  very  careful 
measurement;  and  fourthly,  they  are  arranged  in  rows  parallel  to  the  sides  of  the 
plates,  thus  showing  conclusively  that  they  have  been  produced  in  the  photographic 
manipulation. 

According  to  the  photographs,  sixteen  well-defined  solar  spots  were  on  the  sun 
during  the  time  of  the  eclipse.  In  the  NE.  quadrant,  close  to  the  sun's  limb,  and 
about  90°  E.  of  N.  is  a  remarkably  beautiful  and  characteristic  spot,  greatly  fore- 
shorte'hed  from  its  position,  so  that  the  penumbra  has  disappeared  on  the  west  side  of 
the  umbra  against  which  rest  the  large  bright  facula?,  which  enclose  the  spot.  Looking 
at  it  through  a  lens,  you  are  immediately  struck  with  the  idea  of  a  depression  in  the 

"Since  the  lir.-t  publication  of  this  report  (Jour.  Frank.  lust.,  Oct.,  1*69),  Prof.  H.  Mortou  (Jour.  Frank.  lust., 
Dec.,  181)9)  has  shown  that  tin.-)  "glow"  is  produced  as  follows:     *  *     "  Part  of  the  plate  representing  the  dark 

edge  of  the  union,  anil,  therefore,  not  acted  upon,  furnishes  a  reservoir  of  nitrate  of  silver,  imbibed  by  the  collodion 
film,  which,  during  the  development,  penetrates  for  a  short  distance  into  the  lumiiioiu  area  of  the  sun,  whose  supply 
of  free  nitrate  was  exhausted  by  the  reaction  which  occured  at  the  first  moment  when  the  developer  was  applied." 
My  own  experiments,  given  above,  show  that  the  glow  is  not  subjective,  and  cannot  be  accounted  for  by  irradiation, 
while  Prof.  E.  C.  Pickering  (Jonr.  Frank.  Inst.,  Apr.,  1870)  has  proved  that  diffraction  exerts  no  npprenable  effect  in 
causing  this  phenomenon. 


140  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1860. 

sun's  surface,  and  you  cannot  help  remarking  how  like  it  is  in  appearance  to  a  lunar 
crater,  for  you  are  convinced  that  you  look  down  into  it,  while  the  surrounding  bright 
faculae  give  a  border  similar  to  the  white  walls  of  some  of  the  lunar  mountains.  From 
the  southwestern  portion  of  this  apparently  elevated  ridge  a  large  bright  facula  bridges 
over  the  cavity  in  a  northeast  direction,  and  divides  the  spot  into  two  portions. 

Plates  Nos.  11,  16,  and  21  show  this  object  in  perfection. 

In  the  SE.  quadrant  we  see  three  small  and  w^ll-defined  spots,  and  several 
largely  developed  faculse  near  the  sun's  limb. 

In  the  SW.  quadrant  is  a  large  and  well-developed  spot,  and  near  it,  to  the  N., 
a  group  of  four  smaller  ones.  This  large  spot  exhibited  remarkable  chain  es  during 
the  time  of  the  eclipse,  as  will  be  seen  from  the  drawings  and  measurements  found 
under  the  head  of  "Measurements  on  the  solar  spot  in  the  SW.  quadrant." 

On  close  inspection,  there  is  observed  a  very  white  projection  from  the  surrounding 
bright  surface  of  the  sun,  which  stretches  into  the  northwestern  border  of  the  penumbra 
of  this  spot  and  reaches  nearly  to  its  umbra. 

In  the  NW.  quadrant  no  solar  spots  are  visible  on  the  photographs.  About 
NNW.  of  the  intersection  of  the  threads  of  the  reticule  are  observed  what,  at  first 
sight,  we  might  take  for  a  group  of  spots,  but  they  are  specks  of  dust  on  the  lens  of 
the  ocular,  as  they  change  their  place  on  the  disk  with  the  threads,  always  preserving 
the  same  position  in  reference  to  them.  This  test  will  serve  to  distinguish  other  spots 
on  the  photographs,  produced  by  the  same  cause — as,  for  example,  the  four  spots  on 
the  SE.  quadrant. 

Plate  No.  4,  which,  fortunately,  is  one  of  the  best  photographs,  was  taken 
28.8  after  first  contact,  as  observed  by  Dr.  Gould.  It  shows  a  depression  in  the 
sun's  limb  at  the  point  of  contact,  and  from  this  depression  shoots  into  the  sun  a  high 
lunar  mountain,  whose  position,  measured  from  the  S.  point  of  the  cusp,  is  one-fourth 
of  the  distance  to  the  N.  point  of  the  same.  Mr.  W.  S.  Oilman,  of  New  York,  who 
observed  at  Sioux  City,  Iowa,  informed  me  that  he  determined  first  contact  by  seeing 
this  mountain  peak  thrust  itself  into  the  limb  of  the  sun  before  a  flattening  took  place 
from  contact  of  the  lower  general  surface  of  the  moon.  This  mountain  shows  itself 
on  all  the  photographs  of  the  eastern  limb,  while  other  peaks  appear  as  the  moon 
progresses  over  the  sun.  The  photographs  show  that  the  eastern  limb  of  the  moon  is 
far  more  mountainous  than  the  western. 

Plates  Nos.  4,  9,  and  1 1  best  show  the  mountains  on  the  following  limb ;  plates 
Nos.  31,  35,  and  42  on  the  preceding  limb. 

The  best  method  of  examining  these  mountains  is  to  cut  with  a  sharp  knife  a  disk 
of  paper  of  the  exact  diameter  of  the  image  of  the  moon,  and  make  its  circumference 
coincide  with  the  general  level  of  the  moon's  periphery;  the  lunar  mountains  will  then 
appear  as  black  protuberances  rising  above  the  white  circle  of  the  paper. 

Plates  Nos.  39,  40, 41,42,  and  43,  taken  in  rapid  succession,  as  the  moon  was  leaving 
the  sun's  disk,  previous  to  fourth  contact,  show  two  prominent  lunar  mountains  on  the 
northern  part  of  the  cusp,  followed  by  a  long  depression  in  the  moon's  limb. 

Five  photographs  (Nos.  23-27)  were  taken  during  total  eclipse,  and  one  6".85 
before,  and  one  29S.2  after  totality.  The  one  (No.  22)  taken  68.85  before  the  disap- 


REPORT  OF  THE  IMIILADKU'H  I A    PHOTOGRAPHIC  EXPEDITION.          141 

pearance  of  the  sun  shows  all  the  prominences  of  the  eastern  limb;  but  on  account  of 
the  long  exposure,  the  thin  crescent  of  the  sun  which  then  remained  caused  a  blurring 
of  the  details.  The  picture  is  a  mixture  of  crescent  and  protuberances.  The  promi- 
nences, 6  and  7,  are  entirely  isolated,  while  the  intervening  ones  are  enveloped  in  the 
ght  of  the  crescent. 

Plate  No.  28,  taken  28". 2  after  totality,  is  the  photograph  of  a  very  thin 
solar  crescent,  whose  cusps  are  sharply  defined  throughout.  The  northern  horn  is 
narrower  than  the  southern,  which  causes  the  moon's  disk  to  appear  to  depart  from  a 
circle  curve.* 

No.    24,  taken    at    i3h  52     3".! — that    is.    iys.i     after    beginning   of    totality- 
shows   the   full  development  of  the   prominences  on   the   eastern   limb,   while  on   the 
western  only  the  top  of  the  large  southern  protuberance  (No.  8)  is  visible,  and  a  slight 
glow  appears  on  the  NW.  and  S\V.  border. 

Nos.  25,  23,  26,  and  27, f  taken  respectively  45^.3,  im  8s,  i"1  268.37,  and  i  .  568.2, 
after  the  disappearance  of  the  sun,  show  the  advance  of  the  moon  eastward,  and  the 
gradual  appearance  of  the  prominences  and  glow  on  the  western  limb,  while  those  on 
the  eastern  are  being  gradually  cut  off  from  view. 

In  No.  25,  protuberance  No.  8  is  yet  alone  visible,  while  the  glow  appears  along 
all  the  western  border  of  the  moon.  Protuberances  i  and  2  are  covered  by  the  moon. 

In  No.  23,  the  glow  on  the  western  limb  is  about  equal  to  that  on  the  eastern. 
The  tops  of  protuberances  10  and  i  i  are  just  visible,  while  7  is  just  fading  from  sight. 

In  plate  26,  on  the  western  limb,  prominences  Nos.  9  and  i  2  have  not  yet  come 
into  view:  No.  8  has  already  taken  the  form  of  the  albatross  head;  No.  10  only  ap- 
pears like  a  grain  of  rice  set  on  and;  while  No  1 1  resembles  two  such  grains  standing- 
oil  end  near  each  other.  The  glow  is  now  greatest  on  the  western  limb. 

In  plate  No.  27,  taken  50  seconds  before  the  sun  came  forth,  we  see  No.  8  as  a 
fully-developed  albatross  head  with  bill  and  throat  close  to  the  moon's  border. 

The  small  protuberance  No.  9  now  comes  in  view,  and  No.  10  assumes  the  shape 
of  a  caterpillar;  i  i  appears  as  a  grain  of  wheat  with  a  groove  around  its  middle,  and 
No  12  comes  in  sight.  On  the  moon's  eastern  border  a  mere  trace  of  6  appears,  while 
4  exactly  resembles  a  bird  sailing  close  to  the  surface  of  the  moon.  The  group  of 
protuberances,  No.  5,  which  formerly  appeared  high  above  the  body  of  the  moon, 
floating  in  cloud,  now  rest  upon  its  border. 

This  sketch  will,  I  hope,  give  a  general  idea  of  the  development  and  disappear- 
ance of  the  several  flames,  and  show  how  rapid  was  the  shifting  of  scenes  during 
totality.  All  the  changes  I  have  described  took  place  in  i'"39s.i,  the  time  in  which 
the  five  photographs  were  taken. 

The  diagram  Plate  X,  Fig.  i,  has  been  very  carefully  drawn  from  the  results  of 
measurements  and  calculations  on  the  position-angles  of  the  prominences. 

I  wish  it  to  be  understood  that  all  of  the  measurements  on  the  photographs  given 
in  this  preliminary  report  were  made  on  copies  on  glass,  and  not  on  the  original  iict/a- 
also,  that  no  micrometric  apparatus  was  used,  but  only  an  accurate  scale  divided 

*  Sc.«i  I'hite  IX.  tNo.  a~  is-  uivmi  in  Plate  VII. 


142  ECLIPSE  OF  THE  SUN,  Aldl'ST  7,   ISIi'.i. 

into  halt'  millimeters,  the  readings  on  which  were  made  with  a  lens.  These  numerical 
results  (except  those  of  the  position-angles  and  heights  of  protuberances)  are  therefore 
only  approximative,  and  the  numbers  to  be  used  in  a  thorough  discussion  of  the 
eclipse  will  be  given  as  soon  as  accurate  micrometric  measurements  can  be  made  on 
the  original  negatives. 

The  protuberances  are  designated  by  numbers,  from  i  to  12,  going  from  N.  through 
E.  to  N.  The  position-angles  and  heights  are  tabulated  under  the  head  of  "Results." 

The  drawing  and  measurements  of  the  prominences  on  the  E.  limb  of  the  sun 
are  from  the  first  photograph  taken,  while  those  on  the  W.  are  from  the  last  picture 
obtained.  The  diagram  therefore  shows  the  greatest  visible  development  of  these 
objects  on  the  eastern  limb,  and  those  on  the  western  are  as  they  appeared  50  seconds 
before  the  end  of  totality. 

Proceeding  from  the  N.  by  the  E.  we  perceive  a  glow  of  light  which  begins 
a  little  E.  of  N.,  and  extends  nearly  to  the  S.  point.  This  luminous  fringe  to  the  pho- 
tograph (represented  on  the  diagram  by  the  irregular  dotted  line)  reaches  its  maximum 
height  about  midway  between  the  prominences  2  and  4,  there  attaining  an  ele- 
vation of  2'  15".  Another  maximum  of  altitude  occurs  a  few  degrees  S.  of  No.  5, 
where  it  has  the  same  height.  In  the  midst  of  this  bright  glow  and  near  its  greatest 
height  appears  at  3  and  5  detached  sheets  of  bright  flame  floating  above  the  lower 
.mass  of  the  conflagration. 

The  bases  of  the  other  protuberances  are  on  the  periphery  of  the  moon,  and  all 
except  No.  4  rest  below  the  general  circle  of  the  moon's  border.  This  appearance  is 
ptirtidllji  explained  by  the  fact  that  the  telescope  follows  the  motion  of  the  protuber- 
ances, while  the  moon,  therefore,  has  the  difference  of  angular  velocity  between  it  and 
the  sun  At  the  instant  of  exposure  the  portion  of  the  prominence  resting  against 
the  moon's  limb  is  photographed;  but  as  the  moon  moves  eastward  during  all  the  time 
of  exposure,  the  prominence  will  appear  as  a  (Irjii-cxxioi/  iu  tlic  moon'1*  I'nitb,  for  the  latter 
has  moved  to  a  higher  portion  of  an  eastern  prominence,  and  to  a  lower  portion  of  a 
western,  by  the  time  the  exposure  is  ended. 

From  the  relative  motion  above  referred  to,  it  must  necessarily  follow  that  the 
border  of  the  moon  will  not  be  well  defined;  but  the  eastern  one  will  be  more  sharply 
cut  than  the  western.  All  of  the  photographs  of  totality  show  this  distinctly. 

On  plate  No.  26,  the  apparent  depression  of  prominence  1 1  is  nearly  all  due  to 
its  being  in  the  hazy  limb,  its  base  resting  in  a  very  slight  depression. 

The  amount  of  depression  of  the  prominences  I  have  accurately  represented  in 
the  accompanying  diagram.  (Plate  X,  fig.  i.) 

Proceeding  from  the  north  point  to  the  east,  we  first  meet  with  prominence  No.  i? 
having  the  position-angle  of  about  56°  30'.  It  is  of  the  shape  of  a  rice  grain,  with 
its  base  but  slightly  below  the  circumference  of  the  moon.  In  breadth  it  is  2°  50' and 
in  height  22".  As  i'  on  the  circumference  of  the  sun  equals  124  miles  and  i"  of  arc 
at  the  sun's  distance,  on  August  7,  subtends  449  miles,  it  follows  that  its  actual  dimen- 
sions are  21,000  miles  long,  and  9,900  miles  high. 

Protuberance  No.  2  lies  imbedded  in  the  moon's  border,  and  has  in  form  the  ap- 


REPOKT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.  143 

peararice  of  a  short,  deeply  articulated  worm.      Its  mean  position  is  69°  17';  its  length 
6°  if,  or  46,700  miles,  and  its  greatest  height  equals  22"  or  9,900  miles. 

Between  proturberances  Nos.  2  and  3  arc  two  flames  in  the  midst  of  the  glow 
previously  described;  one  near  to  No.  2,  the  other  quite  close  to  No.  3.  Midway 
between  Nos.  2  and  3  rises  the  diffused  light  to  an  elevation  of  2'  15",  or  60,500 
miles.  The  position  of  protuberance  3  is  87°  15',  and  it  rises  to  a  height  of  i'  15", 
or  33,600  miles. 

We  now  come  to  that  curiously-formed  protuberance  No.  4.  Some  have  com- 
pared it  to  an  ear  of  corn,  but  on  the  photographs  it  appears  like  an  eagle,  with  out- 
spread wings,  resting  on  the  trunk  of  a  tree,  which  leans  toward  the  north.  On  plate 
27,  where  the  tree-stump  is  cut  off  by  the  advancing  moon,  the  resemblance  to  an 
eagle  on  the  wing  is  perfect 

The  form  of  this  object  indicates  instability,  and  impresses  one  with  the  idea  that 
it  is  a  great  traveling  Whirl  of  Hame,  the  direction  of  whose  rotation — as  indicated 
by  the  position  of  the  "wings"  and  the  projection  of  one  on  the  other — is  retrograde 
or  in  the  s;ime  direction  as  the  motion  of  the  hands  of  a  watch.  I  have  examined 
with  care  the  successive  photographs  of  it,  and  although  at  first  I  thought  that  the 
last,  impression  differed  from  those  preceding,  in  that  the  wings  had  become  longer 
and  more  in  a  line  with  each  other,  yet,  on  subsequent  examination,  1  could  not  really 
decide  that  a  perceptible  motion  had  taken  place  during  the  time  of  totality. 

The  position-angle  of  the  north  side  of  the  base  of  this  object  is  96°  25';  its 
height  is  i'  22",  or  36,700  miles,  and  the  spread  of  the  wings,  as  measured  on  plate 
27,  is  9°  31',  or  70,800  miles. 

Protuberance  No.  5  reaches  from  B  to  an  ill-defined  point  beyond  c  of  the  diagram; 
it  is  of  very  irregular  outline,  and  shows  portions  of  its  substance  detached  from  the 
general  mass,  and  floating  freely  above  it,  The  most  elevated  and  bright  of  these 
detached  flames  float  at  a  height  of  at  least.  20,000  miles  above  the  surface  of  the  sun. 
Beyond  the  point  c,  a  white  nebulous  cloud  rises  to  the  elevation  of  2'  1 5",  or 
60,500  miles. 

Protuberance  No.  6  of  the  diagram  has  a  mean  position  of  148°;  its  length  is 
3°  5',  or  22,900  miles;  its  height  is  45",  or  20,000  miles. 

The  position  of  the  center  of  No.  7,  shaped  like  a  grain  of  wheat,  is  159°  22'; 
its  length  5°  13',  equal  to  38,800  miles;  its  height  37",  or  16,600  miles. 

We  now  pass  to  the  western  limb  of  the  sun,  and  meet  with  the  remarkably 
large  and  massive  protuberance  No.  8.  It  is  shaped  like  an  albatross  head,  with  the 
beak  and  under  side  of  the  head  resting  on  the  limb  of  the  moon.  On  a  photograph 
taken  at  Ottumwa,  Iowa,  just  before  the  sun  came  out,  this  protuberence  had  the 
exact  appearance  of  an  albatross  head,  with  the  beak  open,  holding  a  rounded  mass 
between  the  extremity  of  the  jaws.  It  lies  between  the  position-angles  of  230°  13' 
and  245°  46';  its  length  is  15°  33',  or  1 15,700  miles,  and  its  greatest  height  is  75",  or 
33,600  miles. 

The  small  prominence  No.  9  has  a  position  of  273°  27'. 


144  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

Protuberance  No.  10  bears  the  most  striking-  resemblance  to  a  caterpillar.  Its 
mean  position  is  287°  33',  and  its  extends  through  an  angle  of  11°,  or  81,800  miles.. 
Its  maximum  elevation,  which  is  at  the  head  of  "the  caterpillar,"  is  52"  or  23,300 
miles.  Out  of  the  head  issue  two  horns;  the  one  nearest  the  front  being  the  higher 
of  the  two,  and  is  terminated  with  a  knob  or  ball,  from  which  curves  a  broken  line  of 
light  to  the  border  of  the  moon. 

The  center  of  prominence  No.  11  has  a  position  of  318°  33'  and  its  extent  is 
5°  18',  01-37,400  miles,  with  an  elevation  of  44',  or  20,100  miles.  It  lias  the  shape  of 
a  grain  of  rice,  slightly  restricted  in  the  middle. 

The  small  protuberance  No.  12  has  a  mean  position  of  343°.  Its  length  is 
i°  51',  or  13,800  miles,  and  its  greatest  height  is  15",  or  6,700  miles. 

The  faintly-dotted  circle,  inside  the  circumference  of  the  moon,  shows  the  relative 
diameter  and  position  of  the  sun  at  the  middle  of  total  eclipse.  The  scale  on  which 
the  diagram  is  made  fails  to  show  want  of  coincidence  of  the  centers  of  these  circles. 
The  arrow  marks  the  points  of  contact,  and  shows  the  direction  of  the  motion  of  the 
moon. 

7.    RESULTS. 

Under  this  head  I  give  a  few  approximate  results  deduced  from  measurements 
on  the  glass  positives,  it  be'ing  useless  to  attempt  more  until  an  accurate  micrometric 
apparatus  is  brought  to  bear  on  the  original  negatives. 

(a)  The  time  of  first  contact: 

This  determination  was  made  by  taking  the  mean  of  several  measures  of  diameters 
of  the  sun's  image  on  one  of  the  plates,  and  from  the  known  angle  subtended  by  the 
moon  deducing  its  diameter  in  the  same  unit  of  length;  then  the  chord  of  the  cusp 
was  measured,  and  from  these  data  the  distances  of  the  chord  from  the  limbs  of  the 
sun  and  moon  (or  the  versed  sines)  were  calculated 

From  the  known  hourly  motion  of  the  moon  (allowance  being  made  for  parallax) 
we  obtained  the  time  of  first  contact. 

It  is  evident  that  if  this  measure  be  accurately  made  on  the  negatives,  and  the 
effect  of  refraction  be  also  taken  into  account,  we  have  precise  data  for  determining 
the  corrections  necessary  to  be  applied  to  the  elements  of  the  eclipse. 

The  time  of  first  contact  thus  deduced  from  two  plates  gave  i  2''  50'"  2S.94,  which 
is  Is. i  before  contact,  as  observed  by  Professor  Coffin,  and  o".i  before  Dr.  Gould's 
observation.  From  measures  on  another  plate  (No.  5)  we  deduced  i2h  49'"  59",  which 
is  48  before  contact,  as  observed  by  Dr.  Gmild,  and  six-tenths  of  a  second  after  contact, 
as  determined  by  Professor  Young  with  his  new  spectroscopic  method  of  observation. 

(&)  Position-angles  of  first  and  fourth  contacts: 

These  position-angles  we  determined  on  plates  8  and  41  from  the  following 
measures : 


liBPOBT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 


145 


PLATE  No.  8. 

Radius  of  sun  zz  3  1.4. 

Length  of  >£  chord  from  N.  point  to  point  of  contact  =  18.25. 

_  Q     ,—   _. 

5  =.5793  =  sin  35°  24';  X2rr70°  48' 

O      *    i 

Hence  angle  of  first  contact  is — 70°  48'  or  +  289°  12' 
Computed  angle 

Difference. . 


—  o°    12' 


PLATE  No.  41. 

Radius  of  31111  =  30.835. 

Length  of  y2  chord  from  S.  point  to  point  of  fourth  contact  —  18. 

39:|35=>5837_s;n35o43,;  X2  =  7i°  26' 

Position-angle  of  fourth  contact  rr  108°  34' 


Computed  angle •=.  io8c 


o' 


Difference. 


The  points  where  the  inner  dotted  circle  of  the  diagram  is  cut  by  the  arrow  shows 
the  positions  of  contact  as  determined  from  the  photographs. 

((•)  Position -uni/tex  /uid  lir/gJits  of  the  protuberances : 

The  determinations  of  the  position-angles  and  heights  of  the  protuberances  on  the 
eastern  limb  of  the  moon  are  derived  from  measures  on  plate  No.  24,  the  first  taken 
during  totality,  and  those  on  the  western  limb,  from  No.  27,  the  last  plate  of  totality. 

The  measures  were  made  in  the  following  manner:  On  plate  24  only  the  reticule 
line  on  the  eastern  border  is  visible;  but  on  plate  No.  25,  taken  28". 2  after,  both 
eastern  and  western  lines  are  sharply  cut;  and  prominence  No.  6  is  nearly  as  fully 
developed  on  this  plate  as  on  that  just  preceding.  I  therefore  obtained  the  exact 
angle  of  position  of  the  south  side  of  prominence  6,  on  plate  25  ;  then,  from  this 
position,  as  point  of  origin  of  chords  on  plate  24,  I  determined  the  positions  of  promi- 
nences 4,  5,  and  7.  As  the  chords  drawn  from  the  south  side  of  prominence  6  to 
protuberances  i,  2,  and  3  were  too  long  to  give  accurate  determinations  from  their 
measures,  I  fixed  the  position  of  these  prominences  from  measures  made  from  the 
north  side  (point  B)  of  protuberance  No.  5,  previously  determined  by  reference  to  the 
south  side  of  prominence  No.  6. 

On  plate  No.  27  the  reticule  line  on  both  eastern  and  western  limb  is  distinctly 
photographed,  and  so  this  plate  was  alone  used  in  determining  the  positions  of  the 
western  protuberances. 

The  measurements  were  made  on  glass  positives,  taken  directly  from  the  original 
negatives  by  means  of  an  orthoscopic  lens,  which  enlarged  the  moon's  image  to  a 
diameter  of  2.47  inches.  The  plates,  firmly  held  by  a  wooden  clamp,  were  supported 
about  six  inches  above  a  board  covered  with  white  paper,  and  placed  before  a  large 
north  window.  Sometimes  the  plates  were  parallel  to  the  board,  at  others  inclined, 
19  E  s 


146  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

with  the  angle  opening  towards  the  window.  This,  I  found,  was  the  best  illumination 
with  which  to  examine  the  details  of  the "  photographs  and  to  make  measurements 
thereon.  The  legs  of  finely-pointed  dividers  were  clamped  to  the  proper  opening, 
and  with  this  radius  arcs  were  struck  (cutting  through  the  dark  film  of  the  photograph 
to  the  glass  below),  having  as  their  centers  the  points  on  the  moon's  border  cut  by  the 
declination  line  of  the  reticule.  Through  the  intersections  of  these  arcs  a  line  was 
carefully  drawn,  which  gave  the  diameter  of  the  moon's  disk,  which  joined  the  N.  and 
S.  points  of  its  periphery.  Chords  were  now  measured  from  the  N.  and  S.  sides  of 
each  protuberance  to  either  the  N.  or  S.  points  of  position,  according  as  the  protuber- 
ance was  in  the  N.  or  S.  semicircle.  Half  of  a  chord  being  the  sine  of  half  the  angle 
required,  we  can — having  previously  obtained  the  moon's  radius — deduce  therefrom 
the  position-angle. 

These  measures  have  been  made  with  the  greatest  care,  and  can,  I  think,  be  relied 
upon  as  accurate  determinations.  We  do  not  think  that  in  this  case  subsequent 
micrometric  measures  will  add  to  their  precision,  for,  from  the  difficulty  of  defining 
the  exact  boundary  of  the  moon  (especially  on  plate  No.  24),  the  accuracy  of  the 
determination  of  radii  will  not  be  increased  by  attempting  a  micrometric  measure  of 
what  we  cannot  see. 

In  the  measurements  a  finely- divided  millimeter  scale  was  used,  and  the  readings 
were  made  through  a  lens  magnifying  eight  diameters. 

The  adopted  radius  of  the  moon,  on  each  plate,  is  derived  from  the  measures  of  four 
diameters,  inclined  45°  to  each  other.  Every  chord  used  is  the  mean  of  three  measure- 
ments. 

The  measures,  in  millimeters,  serving  as  data  for  the  position,  are  as  follows : 

Plate  No.  29— second  of  totality. 
No.  of  measure.  Diameter  of  moon. 

I 66. 4 

2 66.  o 

3 66.2 

4 66. 2 


Mean  diameter 66.  2 

Radius 33.  i 

From  S.  point  to  S.  side  of  prominence  No.  6 17.  4 

Length  (measured  on  plate  24)  prominence  No.  6 '1.8 

Plate  Ac.  24— first  of  totality.* 
No.  of  measure.  Diameter  of  moon. 

I 66.3 

2 66.  i 

3 66.25 

4 66. 3 

Mean  diameter 66. 24 

Radius 33.  n 

S.  side  of  prominence  6  to  N.  side  of  prominence  7 4.  2 

S.  side  of  prominence  6  to  S.  side  of  prominence  7 7.  2 

S.  side  of  prominence  6  to  N.  side  of  prominence  (point  B)  5 27.  o 

S.  side  of  prominence  6  to  S.  side  of  prominence  (point  C)  5 17.  65 

S.  side  of  prominence  6  to  N.  side  of  base  of  prominence  4 29.  6 

S.  side  of  prominence  6  to  S.  side  of  base  of  prominence  4 28.  75 

N.  side  (B)  of  prominence  5  to  tip  of  S.  wing  of  "eagle"  4 7 


*  See  Plate  IV. 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION- 


147 


N.  side  (I?)  of  prominence  5  to  tip  of  N.  wing  of  "  eagle  "4 6.  2 

N.  side  (H)  of  prominence  5  to  center  of  prominence  3 8.  15 

N.  side  (H)  of  prominence  5  to  S.  side  of  prominence  2 16.  6 

N.  side  (15)  of  prominence  5  to  N.  side  of  prominence  2  ........  20.0 

N.  side  (I!)  of  prominence  5  to  S.  side  of  prominence  I 24.  5 

N.side  (1!)  of  prominence  5  to  N.  side  of  prominence  I 26.0 


Plate  No.  27— the  last  of  totality.' 


No.  of  measure. 

1  .... 

2  .... 

3  .... 

4  .... 


Diameter  of  rnoou. 
...     66.  I 
...     65.9 
•     •    •     65.75 
...     65.9 


Mean  diameter 65. 94 

Radius 32. 97 

S.  point  to  S.  side  of  prominence    8 28.  5 

S.  point  to  N.  side  of  prominence    8 35.  8 

N.  point  to  center  of  prominence    9 45.  2 

N.  point  to  S.  side  of  prominence  10 41-4 

N.  point  to  N.  side  of  prominence  10 36.3 

N.  point  to  S.  side  of  prominence  1 1 24.  75 

N.  point  to  N.  side  of  prominence  12 10.25 

N.  point  to  S.  side  of  prominence  12 9.2 

Table  of  the  position-angles  and  heights  of  the  prominences. 


No.  prominence. 

Position-angles. 

Height. 

Remarks. 

i     

o           /           o           / 

cc      q  to    $7     so 

// 

22 

66     14  to    72     21 

22 

-i 

8?     is  . 

7< 

4  (base  of)  .... 

96     25  to    98       4 

QO       3.Q 

82 

.   IOO       IO 

101     23  to  118    36 

136 

Nebulous  cloud. 

6                   .... 

146     25  to  149    30 

45 

7     . 

156    46  to  161     59 

37 

8 

230     13  to  245     46 

75 

277      27 

10    

282       13  to  293       12 

52 

ii                           ,    . 

3IS       S4  to  121       12 

44 

12                 

342      7  to  343     58 

15 

D 

As  the  moon  glides  over  the  solar  disk  the  angle  of  position  of  any  protuberance 
referred  to  the  disk  of  the  moon  is  constantly  changing,  and  the  amount  of  displace- 
ment depends  on  its  position  in  reference  to  the  line  of  the  moon's  motion. 

The  position-angle  of  the  S.  side  of  prominence  6  was  first  determined  on  plate 
No.  25,  and  this  point,  thus  determined,  was  taken  as  origin  of  chords  on  plate  No. 
24,  taken  288.2  before;  but  I  find  by  computation  that  the  position-angle  of  the 
S.  side  of  prominence  6,  on  plate  24,  is  32'  32"  N.  of  what  it  is  on  plate  25, 
assuming  in  the  computation  that  the  prominence  is  stable  in  form  and  position  on 


*  See  Plate  VII. 


148  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

the  sun's  circumference.  Therefore,  it  follows  that  the  position-angles  of  prominences 
i,  2,  3,  4,  5,  6,  and  7,  as  given  in  the  above  table,  should  be  diminished  by  3 2'. 5  to 
make  them  correspond  to  the  position-angles  they  had  at  the  time  plate  No.  24  was 
taken. 

(d)  Measurements  on  the  solar  spot  in  the  SW.  quadrant : 

The  drawings  marked  "  plate  4"  and  "plate  42  "*  were  made  with  a  camera  lucida, 
the  spots  being  magnified  under  the  microscope  to  exactly  2 1  diameters.  They  show 
better  than  can  be  described  the  changes  which  took  place  in  the  dimension  and  form 
of  this  spot  in  the  interval  between  the  times  of  12''  50'"  58.8  and  i4h  49™  488.8. 
Through  each  spot  two  lines  are  drawn,  in  the  directions  of  the  minimum  and  maxi- 
mum diameters  of  the  spot  on  "plate  42."  The  lines  on  4  are  respectively  parallel  to 
those  on  42,  thus  having  the  same  position-angles. 

On  "plate  4"  we  see  umbra  and  penumbra  of  a  general  circular  outline;  the  intensely 
bright  projection  into  the  margin  of  the  penumbra  is  shown  in  the  depression  in  the 
northwest  border.  The  breadth  of  the  umbra  in  the  direction  of  the  northeasterly 
and  southwesterly  line  is  14". 2,  which  equals,  at  the  distance  of  sun  on  the  7th  of 
August,  6,375  miles.  Its  width  in  the  northwesterly  and  southeasterly  line  is  15". 5, 
or  6,960  miles. 

"  Plate  42  "  shows  the  change  of  dimension  and  of  form  which  took  place  in  ih  59™ 
33",  the  circular  outlines  of  umbra  and  penumbra  having  changed  to  elliptical 
boundaries,  the  direction  of  the  longer  axis  being  northwest  and  southeast.  The 
umbra  has  widened  in  this  direction  4",  or  1,796  miles,  and  has,  in  the  transverse 
direction,  narrowed  its  breadth  5".25,  or  2,357  miles,  while  the  outward  projections  of 
the  umbra  (which  can  be  identified  in  Plate  4)  have  become  greatly  lengthened. 

The  breadth  of  the  umbra  in  northeast  and  southwest  direction  is  9". 6,  or  4,3-10 
miles;  in  the  northwest  and  southeast  line  it  is  19". 6,  or  8,800  miles. 

After  the  drawings  had  been  made  with  the  camera  lucida  a  micrometer  plate 
was  placed  under  the. microscope,  without  deranging  the  instrument,  and  the  magnified 
image  of  hundredths  of  inches  on  the  plate  was  marked  on  the  drawings.  This  gave 
directly  the  value  of  the  magnifying  power  used,  and,  by  computation,  the  value  on 
the  drawing,  in  fraction  of  an  inch,  of  i"  on  the  sun's  disk. 

8.  OBSERVATIONS  ON  THE  APPLICATION  OF  PHOTOGRAPHY  TO  THE  DETERMINATION  OF 
THE  TIMES  OF  CONTACTS  DURING  THE  TRANSITS  OF  VENUS  IN  1874  AND  1882. 

We  here  venture  a  few  remarks  showing  the  peculiar  value  of  photography  in 
the  observations  of  the  transits  of  Venus. 

It  has  been  shown  that  the  sun's  image  was  photographed  on  the  camera  plate 
with  an  exposure  of  only  5J0  of  a  second ;  and  the  duration  of  exposure  for  any 
other  instrument  can  be  determined  with  as  great  precision  by  the  method  which  I 
employed. 

The  instant  the  mechanical  movement  exposes  the  plate  it  also  records  the  time 
of  that  exposure  on  a  chronograph  connected  with  a  break-circuit  clock,  and  thus  we 
have  an  accurately  delineated  figure  of  the  transit  corresponding  to  a  time  marked  on 

*  Plate  X,  Figs.  3  and  4. 


REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.          149 

the  face  of  the  clock  employed;  and  this  correspondence  of  figure  and  time  is  unaffected 
with  personal  equation  either  of  sight  or  of  hearing.  Now,  if  the  error  and  rate  of  the 
clock  can  be  entirely  freed  from  the  personal  equation  of  the  observer  who  determined 
them,  and  if*  the  longitude  of  the  station  be  found  by  the  coincidences  of  the  beats  of 
a  sidereal  clock  with  those  of  a  break-circuit  mean  solar  clock  placed  at  the  observatory 
of  the  first  meridian,  we  have  the  most  accurate  means  of  obtaining  the  absolute  times 
of  contacts  at  the  station  of  observation. 

Thus  we  see  how  applicable  will  be  photography  to  these  observations,  for  the 
data  of  the  solar  parallax  will  be  given  either  by  observing  the  absolute  time  of  the 
ingress  or  of  the  egress  (which  method  is  alone  of  value  in  the  transit  of  1874),  or  by 
determining  the  iln ration  of  the  transit  of  Venus  over  the  solar  disk.  The  photographs 
are  permanent  phenomena,  on  which  we  can  repeat  our  measures  at  leisure,  with  every 
appliance  of  precision,  while  it  is  impossible  to  attain  a  similar  degree  with  eye  and  ear, 
from  the  difficulty  of  micrometrirally  measuring  at  a  precise  instant  the  distance  of 
Venus  from  the  sun's  limb,  and  from  the  (recorded)  distortions  of  Venus  at  contacts. 

It  will  also  be  of  great  value  to  have  a  photographic  record  of  the  appearance  of 
Venus  at  the  contacts,  for  if  the  disk  of  the  planet  then  should  appear  on  the  plate 
to  depart  from  a  circle  and  have  attachments  to  the  sun's  limb,  these  distortions  can 
be  measured  and  allowed  for. 

An  idea  may  be  formed  of  the  apparent  size  of  Venus  during  its  transit  of  the 
sun's  disk  from  the  fact  that  the  umbra  of  the  solar  spot  in  the  southwest  quadrant  is 
15"  in  diameter,  and  that  Venus  at  transit  will  subtend  an  angle  of  about  70";  so 
that  the  planet  would  appear  on  the  plate  as  a  disk  4^3  times  the  diameter  of  this  spot, 
or  as  a  disk  of  .107  inch  diameter  on  an  image  of  the  sun  of  3  inches  in  diameter. 

The  negatives  of  these  photographs  I  find,  from  trial,  will  stand  a  magnifying 
power  of  50  under  the  micrometer,  and  as  i"  of  arc  will  equal  one  seven-hundredth 
inch  on  a  solar  image  of  3  inches  diameter,  we  can,  with  the  above-mentioned  power, 
divide  a  second  into  ten  parts.  This  supposes,  however,  that  the  bisection  by  the 
micrometer  thread  is  on  a  perfectly  well  defined  point,  and  this  does  not  exist  in 
the  outlines  of  any  photograph,  and  especially  is  the  limb  of  the  sun  indistinct  on 
account  of  its  shading,  and  of  the  manner  in  which  the  silver  is  deposited  in  the  col 
lodion  film. 

From  actual  experience  in  measurements  under  the  micrometer,  I  find  that  we 
cannot,  as  yet,  hope  to  make  a  bisection  on  the  sun's  limb  closer  than  one -half  of 
a  second.  On  the  boundary  of  the  umbra  of  a  well-defined  solar  spot  we  can  read 
to  one-quarter  of  a  second,  and  from  this  I  should  think  that  two-tenths  of  a  second 
might  probably  be  attained  as  the  limit  in  a  reading  on  the  limb  of  the  image  of 
Venus. 

But  with  measures  as  close  as  these,  and  the  tables  of  Venus  brought  to  the 
accuracy  which  existing  unreduced  observations  can  give,  we  may  reasonably  hope 
for  a  determination  of  the  solar  parallax  comporting  with  the  most  exact  astronomical 
measures  of  this  century. 

A.  M.  MAYER. 

THE  LEHIGH  UNIVERSITY,  PA.,  September  7,  1869. 


REPORT  OF   PROF.  C.   F.   HIMES,  PH.  D.,  OF  DICKINSON  COLLEGE, 

PENNSYLVANIA. 

DICKINSON  COLLEGE,  August  31,  1869. 

MY  DEAR  SIR:  According  to  request  I  make  the  following  report  of  the  operations 
of  the  section  of  the  photographic  corps  organized  by  you,  consisting  of  Messrs.  J. 
Zentmayer,  J.  C.  Browne,  E  Moelling,  W.  J.  Baker,  and  myself,  stationed  at  Ottumwa 
City,  Iowa,  on  the  Des  Moines  River  and  Burlington  and  Missouri  Railroad  about  75 
miles  west  of  Burlington. 

Our  outfit  consisted  of — 

(1)  The  equatorial  belonging  to  Pennsylvania  College,  Gettysburg,  Pa.,  made  by 
Merz  &  Sohn,  of  Munich,  of  6-inch  aperture,  8)4  feet  focal  length,  with  spring-governor 
driving  clock,  and   mounted  on  a  heavy  wooden  Fraunhofer  stand.     It  was  adapted 
to  the  work  to  be  done,  as  the  other  telescopes  of  the  corps,  by  means  of  a  modified 
Huygenian  eye-piece,  camera  with  spring  exposure-slide,  and  so  forth. 

(2)  Photographic  apparatus  and  chemicals,  in  regard  to  which  a  report  will  be 
made  to  you  by  J.  C.  Browne,  esq.,  who  had  charge  of  the  purely  photographic  work. 

(3)  A  make-circuit  chronograph,  with  two  pens  and  accessories.     Other  astro- 
nomical and  physical  apparatus,  including  chronometers,  was  expected  from  a  co- 
operating astronomicla  party  stationed  at  the  same  place  in  charge  of  Prof.  Stephen 
Alexander. 

We  arrived  at  our  destination  on  Wednesday  evening  preceding  the  eclipse.  On 
Thursday  our  apparatus  was  transported  to  the  point  of  observation,  finely  located  on 
a  bluff  about  a  mile  northeast  of  the  city  by  Professor  Coffin,  and  upon  which,  under 
his  instructions,  a  very  convenient  shelter-shed  had  been  constructed  16  by  1 6  feet,  with 
photographic  dark-room  4  by  9  feet  in  the  southeast  corner;  the  building  in  its  length 
occupying  a  position  nearly  north  and  south.  The  roof  was  constructed  in  six  movable 
sections  of  pine  frames,  covered  with  building  paper,  which  could  be  slid  up  and  down 
wholly  or  partially  very  readily  upon  rafters  projecting  to  the  ground.  According  to 
determinations  from  observatio  .s  by  Professor  Alexander  it  had  a  latitude  of  40°  58' 
12"  N.,  and  longitude  ih  ira  2O8.5  W.  of  Washington. 

The  telescope  was  set  upon  a  cross  of  timber  firmly  let  into  the  earth.  It  was 
soon  discovered  that  the  clock-work,  not  of  very  superior  construction,  had  become 
deranged  by  transportation.  Mr.  Zentmayer,  who  fortunately  for  us  formed  one  of 
our  party,  took  it  apart  and  put  it  in  as  good  running  order  as  it  was  susceptible  of, 
thus  enabling  us  with  care  to  give  the  length  of  exposure  necessary  during  totality 
to  secure  the  amount  of  detail  and  corona  which  our  negatives  show. 

Cloudy  weather  set  in  on  Thursday,  and  on  Friday  morning  a  severe  thunder- 
storm unroofed  a  portion  of  our  shed.  The  sky  continued  overcast  until  about  4 

151 


152  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 

a.  m.  on  Saturday,  when  Polaris  exhibited  himself,  but  for  an  instant.  Regardless  of 
the  depressing  circumstances,  we  continued  such  preparations  as  could  be  made,  with 
apparently  as  much  faith  in  clear  weather  as  astronomical  prediction.  The  adjust- 
ment of  the  telescope  in  the  absence  of  any  assistance  from  the  astronomical  party 
was  mainly  accomplished  by  Mr.  Zentmayer,  but  the  limited  amount  of  fair  weather 
prevented  an  equally  satisfactory  adjustment  of  the  reticule  for  determining  angles  of 
position  photographed  upon  the  plates  with  the  sun.  The  dawn  of  the  ;th  found  the 
sky  still  overcast,  but  gradually  with  a  dry  wind  from  the  east  the  clouds  gave  way, 
until  at  noon  not  a  trace  of  cloud  or  haze  was  to  be  seen.  These  few  hours  afforded 
us  an  opportunity  to  determine  the  actinic  focus  with  great  accuracy,  which,  owing  to 
a  modification  of  the  eye-piece  just  before  leaving  Philadelphia,  had  not  been  deter- 
mined before.  The  chronograph  assigned  to  us  was  by  mistake  left  at  Burlington,  and 
did  not  reach  our  observatory  until  Friday  afternoon.  Upon  placing  it  in  position, 
and  connecting  one  pen  with  the  exposure-slide  of  the  camera  and  the  other  with  the 
key  upon  which  the  seconds  were  to  be  tapped,  it  was  found  that,  although  it  was  not 
in  the  best  condition,  it  could  be  made  to  act  satisfactorily  by  constant  attention.  As 
it  was  necessary,  however,  to  intrust  it  to  volunteer  assistants,  and  there  was  not 
sufficient  time  to  drill  them  properly,  fearing  that  it  might  become  deranged  at  a 
critical  moment,  I  did  not  deem  it  advisable  to  trust  our  record  to  it  alone,  and  imme- 
diately before  the  beginning  of  the  eclipse,  determined  to  make  a  record  of  the  times 
from  a  chronometer  kindly  placed  at  my  disposal  by  Professor  Alexander,  the  correction 
for  which  will  be  found  with  the  annexed  schedule  of  negatives.  I  found  it  very  easy 
to  note  the  fraction  of  a  second  by  the  click  of  the  exposure-slide  during  the  partial  phase, 
warning  -having  been  given  me  before  touching  the  trigger.  I  send  this  record  because 
that  ma,de  by  the  chronograph  is  not  complete,  and,  perhaps,  not  reliable  as  far  as  it  goes 
as  the  instrument  became  deranged  during  the  progress  of  the  eclipse.  During  totality 
an  unforeseen  delay  of  about  a  minute  occurred  in  changing  the  exposure-slide  to  one  of 
full  opening,  and  the  plates  were  afterward  exposed  as  rapidly  as  possible  without  an 
opportunity  to  note  the~time  by  the  chronometer.  Fortunately  the  chronographic 
record  at  this  place,  though  not  as  accurate  as  might  be  desired,  furnishes  very  good 
proximate  data.  Knowing  from  accounts  of  previous  observers  the  liability  to 
encounter  unforeseen  obstacles  at  this  point,  I  had  adjusted  the  chronograph  a  short 
time  before  totality,  and  although  the  seconds  were  not  tapped  during  that  time,  the 
pen  connected  with  the  camera-slide  left  a  very  distinct  record  of  each  exposure, 
and  an  examination  of  the  record  of  seconds  for  several  minutes  preceding  totality 
shows  that  the  fillet  had  a  very  uniform  motion,  from  which  by  measurement  from  the 
last  second  mark  to  the  marks  recording  exposures,  the  times  of  exposure  of  the  totality 
negatives,  as  given  in  the  schedule,  were  obtained.  The  key  by  which  the  seconds 
were  recorded  was  also  used  by  Professor  Alexander  to  note  several  of  his  observations, 
his  records  being  interpolated  between  the  seconds  on  the  fillet. 

It  was  found  necessary  to  increase  the  length  of  exposure  by  detaching  two  of 
the  springs  attached  to  the  exposure-slide  as  the  total  phase  was  approached.  The 
exposure  during  the  partial  phase  was  made  with  the  aperture  of  the  telescope 
reduced  to  two  inches  by  a  diaphragm  placed  over  the  objective.  During  totality 


EBPOET  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION.          153 

the  full  aperture  was  used,  and  exposures  of  six,  twelve,  and  sixteen  seconds  given, 
producing  negatives  of  exquisite  sharpness  and  detail,  including  a  portion  of  the  corona. 
On  account  of  the  unreliable  character  of  the  clock-work  it  was  deemed  advisable  that 
Mr.  Moelling  should  pay  exclusive  attention  to  it  during  the  progress  of  the  eclipse,  in 
order  to  detect  and  correct  any  irregularity  it  might  occasion.  The  general  plan  of 
exposure  was  to  obtain  five  negatives,  if  possible,  near  the  first  and  last  contact,  and 
three  near  the  beginning  and  end  of  totality,  and  at  intervals  of  five  and  ten  minutes 
during  the  other  phases.  Thirty-four  excellent,  accurately  timed  negatives  were 
obtained,  as  given  in  the  annexed  schedule,  in  which  D  indicates  diaphragm  of  two 
inches,  Ffull  aperture;  under  Length  of  Exposure,  under  Drop,  i  indicates  exposure-slide 
with  slit  one-fortieth  of  an  inch  wide ;  2,  with  slit  one-thirtieth ;  3,  with  slit  one-twentieth; 
and  4.,  with  circular  aperture  size  of  eye-piece.  Under  Spring,  i,  2,  3  denote  that  one, 
two,  or  three  springs  were  used  upon  the  exposure-slide.  Lost  indicates  that  the 
negative  is  worthless  by  reason  of  accident  in  manipulation  or  because  the  image  of 
the  sun  is  only  partially  on  the  plate.  The  one  immediately  preceding  totality  displays 
the  limb  of  the  sun  beautifully  cut  up  into  Baily's  beads,  and  the  one  taken  at  the  instant 
of  the  close  of  the  total  phase  received  the  first  rays  of  the  emerging  sun,  and  is  of 
interest  in  this  connection  as  showing  the  red  prominences.  The  first  after  totality 
was  taken  with  the  full  aperture  of  the  telescope,  and  on  that  account  is  much  fogged. 

The  coating  and  developing  of  the  plates  were  exclusively  committed  to  Messrs. 
Browne  and  Baker,  and  the  negatives  obtained  are  photographically  perfect. 

Whilst  we  all  feel  fully  satisfied  with  the  results  of  our  efforts,  the  success  of  which 
has  been  so  largely  due  to  the  thoroughness  of  preparation  in  all  details,  and  the  use 
made  of  the  experience  of  previous  parties  by  you,  we  confess,  with  observers  of  this 
phenomenon  generally,  that  we  feel  that  our  present  experience  would  have  been  of 
great  value.  The  distribution  by  you  of  the  prints  from  negatives  of  last  year  at  Aden 
aided  much  in  regulating  developments  and  exposure. 

The  risk  of  failure,  however,  was  much  increased  by  our  limited  number  and 
limited  time  at  the  place  of  observation. 

We  were  necessarily  excluded  from  extended  observations  beyond  our  special 
work,  but  there  are  several  notes  made  that  may  be  of  interest  in  this  connection. 

I  had  watched  the  approach  of  totality  anxious,  if  possible,  to  obtain  a  negative 
with  Baily's  beads,  and  was  surprised  with  the  sudden  transition  to  comparative 
darkness  at  the  instant  of  totality,  and  the  peculiar  brilliancy  with  which  the  stars 
seemed  to  spring  out  without  the  long  struggle  through  twilight. 

The  corona  approached  much  more  nearly  in  regularity  the  four-rayed  form 
generally  given,  and  which  had  always  seemed  idealized  or  conventional.  The  SW. 
ray  was,  however,  unequally  subdivided  with  the  smaller  part  toward  the  north. 
The  whole  seemed  of  a  fibrous,  slightly  curled  or  twisted  character,  somewhat  like  a 
cirrus  cloud,  and  of  silvery  whiteness.  The  prominences,  especially  the  large  one  a 
little  to  the  left  of  south,  seemed,  at  the  first  instant,  of  a  dazzling  white,  but  after  my 
attention  had  been  diverted  for  a  few  moments,  it  appeared  of  a  brilliant  decided  rose 
color,  bordering  on  crimson,  and  remained  of  this  color  to  the  close.  To  Mr.  Zent- 
mayer,  who  was  engaged  at  the  camera  and  had  used  neither  telescope  nor  screen,  it 

20  E  S 


154 


ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


appeared  white,  with  a  slightly  roseate  hue.  To  Mr.  Moelling,  under  similar  condi- 
tions, it  appeared  white  throughout.  Messrs.  Browne  and  Baker,  who  had  a  short 
glimpse  of  it  from  the  door  of  the  dark  room,  rather  incline  to  the  opinion  that  they 
were  white. 

During  the  progress  of  the  eclipse,  Mr.  Zentmayer,  who  examined  the  ground 
glass  of  the  camera  from  time  to  time  to  notice  the  position  of  the  image  of  the  sun, 
called  my  attention  to  an  appearance  of  small  luminous  bodies  like  meteors  crossing 
the  dark  image  of  the  moon  from  cusp  to  cusp.  Subsequently  they  were  seen  to  pass 
over  the  ground  glass  from  outside  of  the  field  on  to  the  image  of  the  sun,  where,  of 
course,  they  were  lost,  always  coming  from  the  same  side.  We  were  led  by  this 
circumstance  to  regard  them  as  most  likely  to  be  optical  illusions,  perhaps  insects  with 
transparent  wings  or  bodies,  but  the  fact  that  other  observers  report  a  shower  of 
meteors  between  the  moon  and  the  earth,  which  seemed  to  be,  as  far  as  I  can  gather  from 
a  hasty  description,  identical  in  appearance  with  the  objects  noticed  by  us,  our  obser- 
vation may  be  of  considerable  value,  especially  as  Mr.  Zentmayer,  who  saw  most  of 
them,  is  disposed  not  to  regard  them  as  optical  illusions,  since  they  must  have  been 
caused  by  objects  not  less  than  2,000  feet  distant. 

I  cannot  omit  to  mention  the  friendly  manner  in  which  we  were  treated  by  the 
authorities  and  citizens  of  Ottumwa. 

Favored  as  we  were  with  a  sky  free  from  cloud  or  haze,  and  a  beautiful  point  of 
view,  this  phenomenon  left  an  inerasible  impression  upon  our  minds  and  hearts. 

CHARLES  F.  HIMES. 

Prof.  HENRY  MORTON,  PH.  D. 

PHILADELPHIA  PHOTOGRAPHIC  CORPS— OTTUMWA  SECTION. 

Record  of  the  chronometer times  ami 'lengths of 'exposures  of  the  photographic  plates  exposed  during  total  eclipse  of  the  sun,  at  Ottumwa, 

Inua,  August  7,  1869,  as  noted  by  C.  F.  Himes.* 


No. 

Chron.  time  of  exposure. 

Length  of  exposure. 

Aperture. 

Drop. 

Spring. 

I 

2 

3 

4 
5 
6 

7 
8 

9 

10 

ii 

12 
'3 
'4 

15 

h.    m.      s. 
o     ^o     30 

3 

3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
i 

D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 

D 

Lost. 

Lost. 
Lost. 

Lost. 

to     i      c 

TO            2             St 

10     14     57  —  glass  second  quality  ..... 
IO      JO      ^7 

10     28'    c« 

IO      32      5O 

IO      37      28 

10    41     41                    

10     49     22^  —  glass  second  quality  .... 
10     ?s     s6    . 

REPORT  OF  THE  PHILADELPHIA  PHOTOGRAPHIC  EXPEDITION. 

Record  of  the  chronametff  times  and  lengths  of  exposures  of  the  photographic  plates,  etc. — Continued. 


155 


No. 

C'hron.  time  of  exposure. 

Length  of  exposure. 

Aperture. 

Drop. 

Spring. 

16 

"7 
18 

19 
20 

21 
22 

23 
24 

25 
26 

27 
28 
29 

3° 
3i 
32 
33 
34 
35 
36 
37 
38 
39 

h.    m.      s. 
TO     <;6     ^i\4 

I 
I 
4 
4 
4 
I 
I 
I 

I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 

I 
I 

D 
D 
V 

F 
F 
y 

D 
I) 
D 
D 
L> 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 
D 

Baily's 
Beads. 

Fogged. 

10     S7     ^6i£ 

1°     58     33.  32  about  6  seconds   "| 

10     59     19.  76  about  1  2  seconds  I  *-x,p°*ure 
f  Totality. 

II       o     12.  62  about  16  seconds  J 
1  1       4     15     ... 

I 

3 
3 

.  3 

3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 
3 

11         6      12     

ii       6    52    .    .    

ii      7    57%    

ii     10      6^    

ii     16     i6j(£    

II       22      45  J^      

II      2O      27     . 

II     17     ?7!4     . 

II      47      ?8     . 

II        C?          11A      . 

II      C.1      41 

II       54.      12}^     . 

II      ??      12     . 

II      <?      4O     . 

II      56      IO     

II      ?7      58     . 

II      ?Q      54     . 

II      en       75/     . 

D  denotes  aperture  of  two  inches  in  diaphragm  on  objective. 

F  denotes  full  aperture. 

Drop  I  indicates  drop  with  slit  in  slide  one-fortieth  of  an  inch  wide. 

Drop  4  indicates  drop  with  circular  aperture  size  of  eye-piece. 

Spring  I,  2, 3,  indicates  number  of  springs  used  on  drop. 


*The  time  for  No.  39  was  noted  by  chronometer  Daniels  jfr>  "le  reduction  of  which  to  Ottumwa  mean  time  was 
-|-jh  j!m  58'.5;  the  times  for  the  others  were  noted  by  chronometer  Negus  2335,  the  reduction  of  which  to  Ottumwa  mean  time 
was  +5"  50"  s8«.o  (p.  16). 

f  Within  a  second. 


156  ECLIPSE  OF  THE  SUN,  AUGUST  7,  1869. 


The  following  article  from  the  Journal  of  the  Franklin  Institute,  Ixii,  3d  series, 
p.  54,  is  appropriately  introduced  here. — J.  H.  C.  C. 

PHOTOGRAPHING  THE  COKONA. 

BY  PROFESSOR  EDWARD  C.  PICKERING. 

The  difficulty  in  photographing  the  corona  visible  around  the  sun  during  a  total 
eclipse  is  mainly  due  to  its  small  actinic  power.  To  remedy  this  we  must  increase  the 
light  in  our  camera  as  much  as  possible,  and  therefore  when  attached  to  Professor 
Morton's  Eclipse  Party,  in  August,  1869,  I  proposed  that  a  common  portrait  camera 
should  be  used.  As  with  such  instrument  we  can  obtain  an  impression  of  objects  in  a 
comparatively  dark  room  in  a  few  seconds,  it  seemed  probable  that  in  two  or  three 
minutes  so  bright  a  body  as  the  corona  would  produce  a  very  distinct  impression, 
even  of  its  more  remote  portions.  We  found  in  Mount  Pleasant,  where  we  were  sta- 
tioned, two  photographers,  Messrs.  Hoover  Bros.,  who  undertook  to  give  this  plan  a 
trial,  and  as  a  result  they  obtained  a  photograph,  which  is  represented  in  the  accom- 
panying figure  to  double  its  original  size.  I  believe  the  exposure  lasted  during  nearly 


the  whole  period  of  totality,  the  apparent  motion  of  the  sun  being  avoided  by  follow- 
ing it  with  the  camera.  The  aperture  of  the  lens  being  much  greater  compared  with 
its  focal  length  than  that  of  any  telescope,  so  .much  light  is  concentrated  that  an  im- 
pression of  a  large  part  of  the  corona  is  obtained,  giving  one  of  the  best  photo- 
graphs of  this  body  yet  taken. 

A  comparison  with  the  view  taken  by  Mr.  Whipple  in  Shelby  ville  shows  many 
points  of  resemblance,  and  greatly  strengthens  any  conclusions  based  on  either.  It 
also  proves  that  the  structure  common  to  both  is  solar,  or  at  least  not  due  to  any  local 
irregularities  in  our  own  atmosphere.  The  indentation  in  the  moon's  limb  marks  the 
position  of  the  large  protuberance  then  visible,  and  we  readily  perceive  the  bases  of 
the  five  points  or  streamers  which  were  noticed  at  the  same  time,.  The  line  N  S  gives 
the  direction  of  the  sun's  polar  axis,  and  shows  the  increased  height  of  the  corona  at 
its  equator,  and  the  corresponding  diminution  at  its  poles.  The  experiment  is  so  easily 
tried  by  any  photographer  on  the  line  of  totality  as  to  encourage  the  hope  that  in 
future  eclipses,  views  may  be  taken  from  a  great  many  points  Avith  the  largest  portrait 
cameras,  and  thus  eliminating  all  local  effects,  show  with  certainty  how  much  of  the 
corona  is  really  solar. 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY,  May  15,  1871. 


SUPPLEMENTARY  NOTE  BY  PROFESSOR  COFFIN. 

The  photographs  of  tho  eclipse  taken  at  Burlington  have  been  measured  by  Mr. 
Henry  G.  Fitz,  under  the  direction  of  Mr.  Lewis  M.  Rutherfurd,  with  the  apparatus 
constructed  by  the  latter.  Measurements  were  made  of  the  N-S  and  E-W  diameters 
of  the  sun's  disk  as  determined  by  the  lines  in  the  eye-piece  of  the  telescope  (which 
appear  clear  and  distinct  in  the  photographs);  the  vertical  and  horizontal  diameters  of 
the  sun's  disk  when  practicable;  the  distances  and  position-angles  of  the  cusps,  and 
the  distance  of  the  limbs  of  the  sun  and  moon  on  a  line  perpendicular  to  the  line  of 
cusps.  Care  was  taken  to  center  the  plate  to  correspond  with  the  center  of  motion 
of  the  instrument. 

The  photographs  were  taken  with  great  care,  and  every  known  precaution  used 
to  obviate  error  and  secure  work  of  a  high  order  of  precision.  I  had  hoped  to  obtain 
from  them  the  apparent  path  of  the  moon  across  the  sun  and  the  times  of  contact 
with  a  good  degree  of  accuracy.  But  failure  of  health  and  latterly  a  disorder  of  the 
eyes,  which  precluded  the  study  and  arrangement  of  formulas  and  all  work  in  com- 
putations, have  prevented  the  contemplated  discussion.  A  tentative  discussion,  how- 
ever, has  been  made  with  the  aid  of  Mr.  H.  L.  Hodgkins,  of  Columbian  University, 
to  determine  the  times  of  the  first  and  last  contacts. 

For  the  first  contact,  plates  4  to  16*  (see  table  p.  138),  inclusive,  gave  the  chro- 
nometer time  of  i  2h  50™  o",  which  is  almost  identical  with  that  noted  by  Professor 
Young  (p.  44).  But  the  times  derived  from  the  several  plates  vary  from  1 2h  49"'  os  to 
i2h  som  38s. 

For  the  last  contact,  plates  30  to  43  inclusive  give  the  chronometer  time, 
14''  50™  47s;  Dr.  Gould's  being  14''  50™  45"  (p.  36),  and  Professor  Coffin's  14''  50'"  41" 
(p  25);  but  the  several  plates  give  times  varying  from  14''  50"'  30"  to  14''  52'"  o8. 
The  angles  of  position  have  been  determined  from  the  E  and  W  lines  of  each  plate, 
as  the  adjustment  of  the  diaphragm  of  the  telescope  was  made  by  that  line.  The  N  and 
S  line  makes  an  angle  of  89°  30'. 4  with  the  E  and  W  line  from  the  E  point  toward 
the  N  point. 

The  angles  of  position  of  the  normal  to  the  disks  of  the  sun  and  moon,  i.  e.,  of 

the  center  of  the  moon's  disk  from  that  of  the  sun,  on  plates  4  .to    17,  vary  from 

—70°  40'  to  —71°   28',  the  mean  being  —71°    10^2';    and  on  plates  35  to  43  from 

+  108°  5'  to  +109°  3',  the  mean  being  +108°  35'.8,  reckoned  from  the  N  point  of 

the  sun's  disk  +  toward  the  east. 

Correcting  the  measurements  for  refraction  and  for  defective  adjustment  of  the 
center  of  the  sun's  disk  to  the  center  of  motion  of  the  measuring  machine  would 

*  Plates  uumbered  7  and  34  are  not  included  ;  it  is  doubtful  if  they  were  takjn 
21 E  S  1W 


158  ECLIPSE  OF  THE  SUN,   AUGUST  7,   180!). 

probably  diminish  the  discordances,  particularly  in  the  linear  measurements,  but  not 
to  any  great  extent.  The  scale-readings  for  the  moon's  limb  and  the  cusps  are  the 
most  discordant  It  has  been  suggested  as  quite  probable  that  a  higher  magnifying 
power  was  used  in  making  these  measurements  than  the  plates  would  bear. 

Still  it  is  very  doubtful  that  the  most  careful  measurements  and  refined  discussion 
would  produce  results  of  the  precision  desirable  in  eclipse  observations,  and  which 
would  secure  preference  of  photographs  to  eye-observations.  With  all  the  care  possi- 
ble, the  suspicion  will  remain  that  the  development  of  the  plates  may  have  produced 
changes,  very  small  perhaps,  but  sufficient  to  produce  distrust. 

The  Ottumwa  photographs  appear  to  have  been  taken  with  equal  care  with  those 
at  Burlington,  but  imperfect  adjustment  of  the  lines  of  the  reticle  of  the  telescope 
impairs  their  value  for  the  determination  of  angles  of  position. 

It  is  proper  to  state  that  the  original  reports  of  observations  of  the  eclipse  are 
published  as  communicated  to  me  at  the  dates  of  each  (except  some  of  Professor  Alex- 
ander's reports  of  times,  the  changes  of  which  are  noted  in  the  text) ;  and  that  all 
changes  in  the  original  remarks  or  speculations  on  the  eclipse  and  its  results,  when  of 
sufficient  importance,  are  stated. 

In  conclusion,  I  express  my  obligations  to  Dr.  Morrison  and  Mr.  E.  J.  Loomis,  of 
the  Nautical  Almanac  Office;  to  the  former  for  computing  predicted  phases  of  the 
eclipse,  the  latter  for  aid  in  preparing  and  arranging  manuscripts  and  correcting  proofs. 

J.  H.  C.  COFFIN, 
Professor  of  Mathematics,  United  States  Navy. 

WASHINGTON,  May,  1885. 


Solar  fMipM,Auffust  7.  fftM  Sy  Pro r  Coffrfi.Bur/inff fort 


HtfipurfintHff. 


vv 


fly  Pro/1  HJrlson,    M? Mffrsant. 


Fit/.  3 


olnr  Ecffpsr.  August  7  /<¥*,«  By  J>r  OoiiM,Jinrli.ngt«n. 


Pfatt  ff 


fr    m 

I.. 'ill 


/   . 


r  Kflipxi ..lutfunt    7  ItidU. 


I'rof  f  .1.    )'n/i/ir/   K ifr/i/i I//IIH . 

MM 

iliiiiliiiihiiilinili 


r  ai. 


500  600  70O  800  »OU  IOOO  1100  1200  1300  MOO  1500  1600  1700  UOO  19OO  2000  2100 


1900  2000  2100  2200  2300  2400  2600  2600  27OO  2800  29OO  2000  .1100  3200  55OO  3400 


.        <-/ne  mtm/>fl<>  u'ljjttfri    frytrmj  frf/fai/i  f/fti/-  f///fj  ale    Msur 
/;/ir/>f  fiin'.i  in   //if  t/'/l/-   f'Hua  f'ftr'it'  aif  Mfjf   f  f'jfi  i'r</  in  i/tf  .j/trrf;ti//t    /•/ f/if    rfii-fm   t/rta  ///t' 


S,i/dr  AV////.SV  .     .1  uplift    7 ."'  /W6'.<V.       /> in-tin rjti>ii  ,  Ir>wa/. 


PLATE  IV 


l-'rnni   rimtot/raftli   3'C'J-/:  Krf>t>.-mrr  .r>  * . 
nVHUNGTOff  MKAN   TIME    <t"  .1H"L"       OR  It! 'AFTKH  HKC.INXIKC.   OF  TIITsUJTY 


k~^      f\  t?     'lYrr  'a  *» 


OP 


[UHI  VARSITY) 


Solcu-Eclifise. ,  August   7  ?*  1869.      (^ttumii>a/:  Iowa/. 


PLATE  V. 


From  Photograph  N?  18.  Exposure  (5:* 


OTTITMWA       MEAN   TIME    4-f  52?  tfSi'       OR44fAFTKlt  HE G1NKIKC   OJ-'  TOTALITY 
WASHINGTON      ,,  .,  5.      53     54, 


Solar  Eclipse!  Jiugust  7$*  1869.    Oftotrnwa,',  Iowa/. 


] 'LATE  VI. 


OTTl'MWA       MEAN    T1MK     4*'  53*? -JO 

,  ,  .  ,  5  .    M-      +it 


From  Photograph.  Jf"J9.  Exposure*  l-s  w 

07?     /-f.-JJ-i    At'TKK    HKCJNNlNt:  OF  TDTAI.1TY 


Salnrh'r/f/w.    Jm/uKt    7  "' 


VI.ATE  vn. 


From  Photograph  A'?  i'7   /.*.»x'"-s'"/r 


JIVHLINGl'Off  MEAlf  TIMK    4"  r>»?41?  OR  l*SJfAFTKll 
WASHINGTON        ,i  //  5      35     55 


OF  TOTALITY 


7f*  IHti'J.       Ottuniwa.  Iowa. 


PLATK    VI 11. 


From  Photograph  N"20.  Exposure  jffi-"  w 

OTTVMWA     MEAN    TIME      /  f  .7 /  f  l:i  •>        Oft  L'H  *  Bf.TOItf:'  THK  f:.\D   Of  TOTALITY 
,  .  ,   .  .i       55.     H3. 


Solar  Eclipse-,  .Ini/nxi  7.  lilli'.i. 


Prof.  A.M.Mtii/er.  liurlimjton ,  lown . 


Plate  X. 


X 


E 


S 


Plate  15. 

4h.    21m.    18.9  s. 


Fy.3. 


Fy.4. 


-E 


Plate  4. 

3h.  ~id  in.   14..") 


t  .....     i     ; 

CT  1O'      •     20*     •     3O* 


1  ori  drawings  =.027  inch. 
Ion  the  Sun  =  449   miles 


Plate  42 . 

,r)h.55m.  38. 


UNIVKKSITY    OF    CALIFOKMA    l.lliUAKY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
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